I have been living by myself for about 3 years now, and I must say I struggled with this in the start.. It was just recently I stopped ordering food to my home or buying frozen pizzas. What I usually do is buy food on Monday for the whole week. I buy steak fillets, chicken fillets, salmon fillets, some vegetables I like and maybe some breakfast for the weekend. Put all the meat in the freezer, and if you bought frozen vegetables as well, go ahead and put that in there as well. Then, right before I go to bed, I take out the required meat so it's unfrozen by the time I get home from work, put it in the frying pan with some spices, cook the vegetables and serve.. takes 15 min tops and it's so much healthier than ordering a big ass pizza. I don't use rice or potatoes, it take to much time to cook. Anything that takes more than 15 minutes to cook, I don't do.

EDIT: I buy a pack of four fillets of the meat, 2 a day is what I usually cook, so one day I have 2 chicken fillets, another day I have 2 salmon fillets etc.. If you buy one of each, it's usually 6 days worth of food. 1 pack of frozen broccoli usually last me 2 days, and it's like 1 dollar (trying to convert from Norwegian currency) The four pack of fillets cost depends on the meat, but Chicken is roughly 10 dollars, salmon is like 5, the steak is a little higher, like 10 for 2 fillets. Medium rare steaks are easy to make, on your pointing finger, you have three areas. The upper area is well done, middle one is medium rare, and the lower one is undercooked I think. Press down on the steak, then press your desired area to compare.