Start your list now as you think of them. For example, a bic-type long click-lighter, fat wood starter sticks and a poker if you like campfires. (Leave firewood at home, though, because many states ban bringing it in due to insect infestation.)
Depends on your interests. If you hike, bring good-fitting shoes, quality socks, a sun hat you like, etc.
Think about the things that would be harder or time-consuming to find en route. Electronic chargers for phones, iPad, camera. Those go on the list.
I like to bring important info in the event something happened back home - such as our home insurance agent contact info and policy number. Copies of our passports, etc. etc.
If you like photography, plan ahead on how you'll save your images as you go so you don't lose them all if the camera is lost. Extra SD cards, accessories. I have an accessory to download from the card onto the iPad, and then we can look at photos together. HDMI cable to watch them on RV TV.
Some sizes of batteries are hard to find. We tried a batch of WalMarts looking for one to use on the remote clicker to open the RV cab doors when one went bad, never could find the right size. So we keep an extra to bring along.
Fuses and RV-specific mechanical stuff is a whole other topic.
Another vote for WM in general, though. You can find easily them around US and Canada, they have a lot of odds & ends, and it's easy to park. We tend to have a WM list going most of the time while on our trips, and if it's a Super Wm, you can get groceries, too.
DH's rain jacket went missing somehow a week or two into a five-week trip, and he found a very suitable water-repellent black leather-look jacket with a hood at WallyWorld for about $25. Sure came in handy this summer on rainy, cool days while setting up or getting ready to leave a campsite.
