Looks to me like you have an advantage over a lot of folks who have the use of legs and don't exercise. They won't know they have limitations until it's too late. You have one you live with daily and have adjusted your life to accommodate.

Two things got my attention in your initial post: "manual wheelchair", "no lift". IMO, by not falling into the trap set up by technology, you did yourself a huge service. Electric wheelchairs and lifts require battery power; instead you have upper body strength.

Do you need elevators to get to/from your office? If so, how will you get from your office to your van when the power goes out? Maybe your building has a back-up generator and it's not an issue, but if it is, supplies in the office which would allow you to bug-in there might be appropriate. You know the situation, your call.

Look at the different situations that could arise with your vehicle and at work. I have the Powerflares mentioned previously in my truck because in SOCAL with all the wildfire danger, they seem like a better option than a road flare. Great signaling device and they won't start a fire next to your van. I'll assume you have blankets in the van and you always dress appropriately. You already carry so that's covered too. (I hope you get enough trigger time, but that's an issue for another forum.)