I just got back from DLR in July and have now added an essential item to my list of things I carry with me: toilet paper!!
The t.p. at DLR is so bad that I will carry my own from now on.
Like many others, I carry zip lock baggies, not to protect things, but to collect leftovers. If it's a cool day I bring large black garbage bags too, to poke a "head hole" in and wear on the wet rides. Most other items I carry have already been mentioned. For those of you "tutting" about the amount of things people bring, my friend has a saying: "Better to have it and not need it, than to need it and not have it!"