I used to waste food too much when I lived on my own ... similar pattern of optimism/buying fruits/veggies that spoil quickly, then having stuff come up, going out to eat instead, and not cooking the food in time. (I also don't enjoy cooking, so that didn't help.)
Now, my husband and I have gotten into a good groove where we hardly ever eat out, and waste very little food. Every week, we buy stuff for salads (lettuce, veggies, & bacon), and stuff for sandwiches (cold cuts, sliced cheese, bread). We buy apples, clementines (aka fruits that keep well), heartier veggies for snacking like heirloom tomatoes and snow peas, I buy frozen raspberries (since they're ripe year round and delicious). We buy some stuff that lasts a long time - granola bars, nuts, tortilla chips, etc. Lots of frozen veggies, and bulk-buy meat at Costco and freeze. I'll make soup or some similar dish, and he'll do something with rice/quinoa/pasta and veggies and spices. He's really excellent at combining things we have around, which I suck at. We don't have so much stuff in the fridge that it goes bad because we forgot about it.
WTF @ people who don't do leftovers ... I like my free time, and would never want to cook/prepare food every day. Leftovers are where it's at! Since I have no issue eating the same thing many days in a row, I've never had any aversion to leftovers.