Emergencies with disabled people need to be thought out well ahead of need. On foot overland, is simply out of the question.
Regular wheelchairs are bulky and heavy. You might consider getting a folding one like this
http://support-mobility.drleonards.com/Support-Mobility/Wheelchairs/Deluxe-Travel-Chair/25056.cfmMy Mom had one of these and they are great. They're sturdy, they fold to 8" wide, and weigh just under 30 lbs. You want to have a flat gel pad to go with it. Yes, they have small wheels, but two people can lift the chair with occupant fairly easily if the person isn't too big. My sister and I carried Mom up steps in hers.
If the big wheelchair is something you need to keep handy, consider getting a carrier for it that fits on the back of the car, that either folds down or can be attached in a hurry.
If oxygen is an issue, try to have more than one source. The most common are the machines, but they do need electric. If there's a reasonable chance you will be evacuating to a site with power, take it. You might want to keep a portable unit for power outages and travel. I always kept 6 or 7 of the small tanks handy. The big ones are a real pain to deal with.
Medications are often critical. Murphy's Law says that a disaster will occur with minimal meds available. Try to get a supply at least 30 days ahead. Don't let anyone tell you that you can't do this. It's the insurance company that won't allow this, not your doctor or pharmacist or any law. Talk to the disabled person's doctor and explain what you want to do. The doctor will usually write out an extra prescription, but it has to be paid for as a non-insurance-covered item. Start with the most critical, on the doctor's advice.
Type out all the pertinent information on the patient's medical conditions, who the doctors are, their addresses, phones & fax numbers, SS info, current meds and dosages, and any
drug allergies. Label it as MEDICAL INFO FOR JANE SMITH with a red felt tip marker, and seal in a clear, waterproof container.
Keep enough special foods and favorite comfort foods in a quick-grab container. Consider stocking some Ensure.
Don't forget some entertainment, paperbacks, lg print books, books on tape, etc. My Mom loved those little $10 electronic poker machines. Got extra glasses? Take 'em all!
Favorite or special pillow, fuzzy blankets, water bottle, personal care items, lots of handi-wipes or bath-wipes, a roll of soft paper towels (like Viva).
Pay attention to what the person needs and uses every day, then be ready to provide it or a good substitute.
Always keep in mind that it's bad enough to be in a disaster situation -- how would you feel if you were disabled, too?
Sue