The following is based on my personal, non-confined experience as a semi-regular wheelchair user. Another wheelchair user probably feels differently about their own experience.
Questions and statements I often hear from strangers in public when I'm using my wheelchair: "Why are you in a wheelchair?", "What's wrong with your legs?", "Why are you in a wheelchair if you can walk?", "You're too young/too good looking/not disabled enough to be in a wheelchair," "I was in a wheelchair for two weeks once; I know exactly how you feel."
Truthfully, it's none of your business. I know most able-bodied people have good intentions when trying to relate to me and my wheelchair. Questions and statements are fine with me, but please think before you ask. "How do you like the weather today?" and "It sure is chilly in here!" are perfectly acceptable. They are the same conversation starters you would use for anyone else. If I want to talk about my wheelchair, I will. Personal questions aren't usually chitchatty. It takes a lot of energy for me to chat with strangers, especially when travelling.
"Do you need help getting to/on/off/away from the airplane?" are questions I like to hear from airport staff. Travel can be exhausting and awkward and their particular offer of help is always welcome. Someone zipping to my side from across the room and grabbing the purse I dropped while saying "HERE LET ME HELP YOU!" is unnecessary. I'm capable of picking up something I dropped and will ask for help if I need it. I appreciate that people want to help, but please don't assume that, just because someone is in a wheelchair, they are automatically helpless. I am a human who is sitting down and can often get more done than a non-wheelchair user might speculate. No pity necessary!
Additionally (this is important): If you are not disabled, please don't camp out in the handicapped stalls in public restrooms. I recently had to abandon my chair in the aisle (a privilege not all wheelchair users have) and awkwardly use a standard stall because an able-bodied person was taaaaking her tiiiime in the only handicapped stall with her toddler instead of using a standard stall or a family bathroom. I personally understand that taking small children to the bathroom is a feat in and of itself, but remember that, more often than not, a disabled person's *only* option is that stall. Able-bodied people have more choices. Get in, get out! We're all trying to get where we're going without peeing our pants.