For friends it seems that sincere praise / avoiding criticism would be good, but what would you recommend as rewards to self? I'm pretty sure that nicotine and pizza slices would work for me, but I'm also sure that those aren't things I want to do more of.

M&Ms, one piece at a time -- they are small enough. (It would probably be good if you stop eating them in all other circumstances, but that is not big sacrifice.)

Or try a symbolic reward. For example put on your table two glass boxes, put 100 stones in first one, and every time you want to reward yourself, move one stone from the first box to the second one, and congratulate yourself on progress. When all stones are in the second box, give yourself a big reward (pizza or whatever), change the boxes, and start again. (This way the reward is still linked to pizza, but it is less pizza. And you see your progress all the time.)