My only real expense is food. I need to eat well, and a LOT to keep me going, but I also want to eat cheaply so I can keep cycling as long as possible. Here's my tried-and-tested eating routine. I eat around 4000 calories per day (about double the recommended daily calorie intake for a woman) but I don't count specifically or anything.
Foods I try to keep with me:
Milk subsititute - keeps much longer than normal milk, especially in black panniers in the heat
Indian spice mix
Canned tomato or passata
Canned chick peas
Coffee - made in trangia kettle, with rice milk and agave syrup or sugar (I take a few extra when I get coffee sometimes during the day, sneaky). My friend showed me that you can make pot coffee with nice ground coffee, literally just by bringing the water to boil with the coffee in, and then leaving it for 5 mins to settle and brew. The grounds sink to the bottom and you can pour it out just fine!
Porridge - depends on what I can get in the locality, but bio shops usually have rolled oats if normal supermarkets don't. at the moment I'm mixing the fibrous outside grain with oats, which needs a bit of soaking before cooking. I make it with a splash of rice milk and mostly water. Then add a bit of rice milk at the end. I add a sliced banana and sultanas or raisins or other dried fruit, and agave nectar.
Lunch & Dinner:
I gave up on sandwiches a while ago, since I find the stuff I need really hard to maintain, and it seems to take up a load of space, and never really fills me up. So depending on the heat, I either make double lunch and then eat it for dinner too, or make double dinner and then eat it for lunch the next day.
I alternate between a pasta thing and a rice thing. Usually:
Pasta with pesto and some veg
Pasta with tomato and some veg
Tiny pasta with tinned fish and salad (my fave with rocket)
Indian curry with chick peas and tomato and veg and rice
Moroccan-type curry with chickpeas and veg and rice (or sometimes couscous)
I'm a huge snax-er always and forever. I eat mostly chocolate, cookies, biscuits and cakes, fruit (usually sneaked from orchards or picked up from roadside sellers) dates, whatever. Forever and ever amen.
I'm always looking for more food suggestions, and I'm sure this routine will evolve as the food changes throughout the world.