It's kind of a no-brainer to seek out happy hours whatever age you are, but it's even easier on a student schedule. Keeping odd hours means that you have more flexibility to attend more happy hours, and it's a good (cheaper) way to keep up with your job-having friends. Do a bit of sleuthing and see what's out there. Some places have late-night happy hours as well, if getting blotto at 6pm isn't conducive to studying. There's no point in paying full price for socializing if you can find a legitimate way to get a discount. Make and keep a list of your favorite happy hour haunts and float it to your friends.
I'm not talking about dumpster diving, but if you're in a free food situation, find a way to take some of that home with you. A friend of mine used to carry around tupperware and would load up on any free food she ever came across. That's the extreme end of the spectrum, but if you are ever in a situation where it's suggested that you take food home--do it. Just make sure you eat it. One of my jobs in grad school was at a fancy private library that hosted a lot of functions. I never had to bring lunch. Yes, sometimes my lunch would be chips and an ice cream sandwich, but it was free, so who cares.
Grad students keep odd hours, and are often traveling from class to work to the library to social events. I can't even count the number of times when I've realized that I'm going to be out of the house for 12-14 hours and haven't even thought about what/when I'm going to eat. If you have to eat on the go, you'll probably have to rely on fast or convenience foods which can really get expensive after a while and aren't particularly good for you. Instead of doing that, spend a little time and effort and plan ahead.
If you have a job stash some healthy snacks there, so you'll always know you have something. My go-to is instant oatmeal in the single serve packs. I keep a box at work, and a packet in my purse at all times. I can't count the number of times I've arrived at work, realized I've forgotten my lunch, and had to rely on that oatmeal. It's filling, and it's a hell of a lot cheaper than going out to get something.
In your backpack, always keep a variety of snacks. Buy or make granola bars, carry apples or oranges (handy, portable and healthy), buy dried fruit snacks, buy or make trail mix, carry around goldfish crackers--anything you like. Then, when you realize that you've been holed up in the library for ten hours and haven't eaten, you don't have to go to the vending machine or cafe. You have to carry a backpack anyway, might as well put food in it. A couple I went to grad school with always had a snack bag. It was just a giant freezer bag with a variety of snacks in it, and they never had to go to the vending machine.
This is just good advice for everyone, not just grad students. Never get caught without food. Life is unpredictable, and you never know when you're going to need a snack. Presently, at Job #1 I have a box of single-serving oatmeal, some figs and an odwalla bar. At Job #2, I have a bag of trader joes peanut-butter filled pretzels, an apple and some goldfish grahams. In my car, I have granola bars. In my purse, I have oatmeal and dried fruit snacks.
Of course, carry a water bottle with you as well.
Food in General
Food is the biggest part of most people's budget, but one that can be greatly reduced with a little pre-planning. Much like making sure you always have a snack, when you're a grad student, make sure you always have something ready to go. Pick a day in the week when you can do the bulk of your cooking and have plenty of frozen meals on hand. Even if you've eaten a couple snacks while in the library, you will most likely come home starving (learning takes a lot of energy), and that is a recipe for pizza ordering. If you take a little time, say on a Sunday, to figure out how many meals you'll be eating at home, and pre-make whatever you can. This could be anything from making a pot of soup and freezing individual portions, to pre-cutting veggies to making sure you have bread for sandwiches.
If we're being completely honest, while I was in grad school, I ate a lot of frozen pizza and boxed pastas. They weren't very good for me, but they were quick and easy, and cheaper than going out. If you want to be healthy, pre-make yourself some pizza and freeze it; make some pasta sauce ahead of time so you just have to heat it up and cook the noodles. Your shortcuts will be based on what you eat, but always be thinking in terms of planning ahead. It's a bit tedious at first, but becomes second nature quickly. Plus, it's nice to focus on something besides school sometimes.
Stay tuned for Grad School on a Budget Part 2...