2 Questions!
1: How many days does it usually take to run out of food, if used rationally and with books?
2: How many days does it take of nonstop killing to get the Real Mega Buster?
Good questions,
1. Normally, 4 days(at least how I played) But with every single book that you can collect all you would need is any kind of food that could heal at least 3 HP(without books) would then heal full HP. EX: Books that could help you and how much they heal combined with certain foods: Health-50%, Health 1-50%, Survival-100% + Raw Meat-3HP = 9HP Of course with everyone trying to kill you, It may be hard to collect these books. But if you manage it, your good awhile.
2. Now, if your going for Genocide Award, dont try it with Infinty Mode, just go into 72 Hour Mode and take the maitenance tunnels with some cars until you get the award. For me, it took about 3 days(Real time) with long intervals of break(I only played about 3 hours a day). But it was worth it.