I am but a lowly section hiker, a peasant really. I bow at the feet of the mighty thrus and am thankful everyday when they acknowledge my existence. So knowing that I'll throw out whatever tiny crumbs of wisdom I can.
In all seriousness though (I'm in a weird mood today...sorry), see my input below.
Actually can't help out here too much as I use alcohol, but I can say that on most of the trail canisters are fairly easy to come by.
I don't use toothpaste.
I've gotten rides before, and do not offer tips. I have paid it back though by giving thrus rides into town.
This one depends on the lay of the land and the local regulations. In a good portion of the South (not including GSMNP and SNP) there are usually camp spots in close proximity to shelters where if you get to the shelter and it's full you can typically hike a little further up or back and find something. Often times you could just hike into the woods off trail and make camp too. There are many areas of the trail where camping is prohibited except for in designated spots (GSMNP, SNP, the White Mountains, MA, CT, and some other areas), and you would likely have to stay in the shelter there. As others have mentioned bring ear plugs. I also like to use a sleeping mask if I'm in a shelter because then people turning on their headlamps doesn't wake me up.
Can't offer a lot of input on this one other than to say that very few people use a Ursack on the AT. Most areas that have bear problems have storage provided (cables, boxes and/or poles). For areas that don't you can usually hang a normal sil-nylon drybag using the PCT method.