Simple carbs, especially baked sweets. I'm a sucker for a good cookie, brownie, or piece of pie. I find it especially hard to avoid them when I'm overworked and overtired. It's been tough this winter as the lack of outdoor exercise and an abundance of extra hours at work, have resulted in a lot of unnecessary munching.
Caffine is my second worst food vice. I've quit it several times but always seem to get started again during the short days of winter. Without it, I'd hibernate like a bear. In the summer, I really don't need it.
My third vice is spending way too much time online when I can't be out riding.