After a couple of weeks of ridiculously warm (20+) and sunny days, it was a very fast change. And already we are back to very sunny days and highs approaching 20C.
This kind of radical temperature change is something to consider when preparing an evacuation kit. Some people I know totally repack their equipment for different seasons. I realize that different parts of the world have vastly different climates but I do think it is important to try to maintain a more all season bag rather than too much of a season-specific one. One simple reason is that you might forget to repack it for the next season or just not get around to it - I am pretty sure procrastination is my middle name at least. Additionally for where I live, similar to many parts of Canada, rapid weather changes and extreme temperature fluctuations are not uncommon. Does it snow in summer a lot? Maybe not but we do usually get a little snow, even in July or August and it does occasionally occur even in the southern parts of the country (snowed south of Edmonton this week). And even if it isn't actually below freezing, much colder weather than the norm can always happen.
You must also consider overnight temperatures which can be exceedingly cold compared to daytime weather. When I see the way some people pack for "running for the hills" I suspect their camping experiences were some combinations of:
2. So long ago they might as well be never
3. Car camping
4. Using an RV
5. "Roughing it" in a cabin with a woodstove/fireplace
6. Summer weather that worked out for them
It's like they've been cold or wet before, even when camping! Lucky people perhaps, but I have a hard time imaging how they could even manage living in an improvised shelter let alone in the bush with such limited gear and clothing. When packing an evacuation kit, you should consider the worst case scenario - wet, freezing cold, etc, rather than always go for the lightest items possible. It's a lot easier to jettison extra items than go back and get what you didn't bring.
Why do I keep saying evacuation kit rather than BOB (bug out bag)? A lot of the BOB examples I see online are based on a more grab-and-go small bag and seem to cater to an American audience - they are centered around firearms. Not that I'm opposed to the idea but grabbing your guns and taking off with them is more complicated in Canada and a lot of the best portable weapons are illegal. Additionally, the weapons based gear kit is for defense against people, it's not necessarily of much other value. Plus that kind of BOB doesn't address pretty much the most important thing you should consider for evacuating - clothing. I can build some pretty decent shelters, I can potentially scavenge for some food or just starve for a long time (it works for many situations), there is lots of water here, etc, but I can't imagine trying to make clothing. And even if I somehow become the mighty bushman and killed a moose with my teeth, I have no idea how to make clothes from it!!
Our Evacuation Kit
What I have is backpacks pre-packed for all of us (also useful for camping trips). This is the main evacuation kit item and is relatively grab-and-go. I also have some very large duffel bags with extra clothing and various other useful items - they can be thrown into a car but wouldn't be something we carried with us if we were walking out. Unfortunately, due to the bulk of some items and the cost of good gear, we don't have duplicate sets of our best boots and extreme winter clothing. We actually wear that stuff in winter. If we weren't able to grab it at the front door, we would have to make do but we would be in trouble. I hope to improve on that over time or just move somewhere warmer, hehe.
As for what you should focus on, clothing-wise, it's always best to remember the old standby - layers. Layers provide the most effective way to maintain your core temperature and since you are planning for an evacuation that could happen at any time under any sort of conditions, clothing layers provide you with options suitable for more situations.
There are far better explanations out there than I could provide about maintaining core temperature, I would suggest you read Cody Lundin's book 98.6 Degrees: The Art of Keeping Your Ass Alive.
Obviously your clothing choices will be affected by where you live. Someone living in Florida is looking at different weather possibilities than someone living in Nunavut, so I'm not going to jump in with a whole bunch of useless advice but I will add in a few reasons why I value layers, for my personal situation. I live in Canada's arctic, in the treeline. There is a lot of water, brush, stubby tress, etc and there is snow on the ground for about 9 months - my main priorities are: keeping dry, keeping warm, and keeping hydrated.
It's a very short summer season here and it's rarely warm enough in any 24-hour period for warmth not to be a consideration. Even a small wind change will blow in cold moist air off the arctic ocean. Dry is always a consideration and hydration is obvious. I need clothing layers that are waterproof and can add some bug and sun protection while allowing for venting to keep me from overheating.
Winter temperatures are frequently below -40 C (huh, that's also -40F, what a strange system) not counting wind chill. Working hard in cold weather with all your gear on makes you sweat, which is a great way to kill yourself. Drying out wet clothing in winter requires a lot of heat. Fire-making materials can be hard to come by in my immediate area and are nearly non-existent past the treeline (driftwood along the ocean coast and trees/brush along the river). Again, being able to reduce and add layers as needed is a simple way to regulate core temperature and similar needs apply - I need waterproof clothing preferably with some way of venting heat.
Comfortable, waterproof boots are a must, winter or summer. Running shoes are a waste of time here. Get the boots large enough to allow for a double sock.
What I would consider as your no-shit must haves for an evacuation where you might actually have to live in the bush are:
1. A proper set of clothing and good boots.
2. A cooking pot
3. A good knife
4. A way to make fire
Everything else is gravy. Very useful gravy mind you....but gravy.
A few extra items that I find useful:
Hand and foot warmers - they can be a literal lifesaver, or a toe saver at least! Cheap and weight next to nothing.
Sunglasses - an absolute must here, snow blindness is not BS and 24-hour sunlight makes it an obvious need. Get wrap arounds, helps with wind protection too.
You can never have too many spare (dry) socks.
Bug net clothing - pants, jacket or, at the very least, a head covering. The head covering is so small you can leave it in your bags year round so you never forget to add it. The bugs have to be experienced to be believed here and bug spray is of limited effectiveness and can run out.