Tips for the frugal PhD student

I've often seen requests from PhD students who are forced to live on a small salary, often in an expensive city, with little time on their hands. Though I'm lucky enough to live in a place where the cost of life is pretty low, I've accumulated a lot of experience in this field and thought I'd share some tips. Mostly it comes down to the fact that your time and health are valuable and that frugal decisions should keep that in mind.
* Tips to make some extra money
* Participate in research studies. All research universities have them. They are usually held in the Psych department, Neuroscience, Med School or Business school. You find out about them either from fliers or by signing up for a list-serve or website. Be selective. I pick studies that pay a lot for the time investment (like fMRI studies) or studies where I get paid a little and get an added bonus feature (one was on meditation, the bonus was that I'd get less stressed; another was on negotiating techniques and I learned a useful tool while being paid 40$/h). I never do medical studies where a drug/device is being tested unless I think it's absolutely worth it (I did a dental school one where they paid me to use their electric toothbrush for a month).
* Tutoring Tutor in a subject that you've taught/been a TA for in the past so you don't have to spend any time familiarizing yourself with the course structure/materials. Decide how much you'll charge an hour and don't accept people willing to pay less. Be very selective and don't take on more than you can. For the love of God, don't tutor in your office if you have office mates. Go to a coffee shop or study room in the library.
* Bank account bonuses Many bank accounts will give you a bonus for signing up and meeting certain criteria. This is something I recommend to PhD students because they'll usually be organized/detailed oriented enough to follow through with the steps necessary. I opened two last year and made 500$ for maybe 10 minutes of work. Some have a direct deposit as a requirement, but there are websites on the internet that compile lists of things that count like direct deposits (like a paypal payment or pushing transferring money from another account)
* Renting your room/apartment out for graduation weekend or any big events that might be coming to your city/town. Airbnb is a common choice, but advertising on local social media also works. If you like nature you can spend those days camping, otherwise you can visit friends or family, or stay with a friend and split your profits with them.
* Ebay/Craiglist selling again, you have to be very selective. One thing that works if driving around apartment complexes in April/May or August and picking up good items that are left behind by students moving out. Only pick up things that you think will sell easily, like mini-fridges. Then turn around and sell to incoming students. You can also do this with textbooks- use an app to see how much it's going for on ebay/amazon and only pick it up if you can make enough profit to justify your work.
* Credit card bonuses This is another piece of advice that I only recommend for people who are very good at paying attention to details. Don't recommend it to folks who are bad at finances or have a bad credit history. It goes like this: you get a cc with a very high signup bonus. You time it just right so that you can charge reimbursable expenses on it (conference travel, meals for applicants during interview week, supplies for your lab if you're allowed to purchase them yourself etc.). You meet the minimum spend on the credit card and other requirements for the bonus. You always pay your credit card in full. Use bonus for your personal travel so you don't have to spend any of your money on planes/trains/hotels.
* Ways to save money
* Have a plan for lunches you will have days in which you fail to prepare a lunch or bring leftovers. Have a plan for those days to avoid spending money on crappy overpriced food. I have some soylent powder stashed in my office with a blender bottle. I also have a few tiny cans/packages of things that will be good in a salad (olives, beans, walnuts, almonds, corn). If you have these you can buy just the greens at the salad buffet and spend almost no money because they don't weigh much. Or you can pick them from your campus' edible gardens if you have those.
* Use your campus' gym. you are already paying for it, you should use it. Breaking up your day with some exercise will keep you sane and healthy in a stage of your life that will slowly chip away at your self-worth. Using the shower/towels afterwards saves on your bills as well, and gives you a boost of energy if you go in the middle of the day.
* Free food events there are often mentioned on these threads. Only go if the event itself is appealing and worth your time. A cold wrap is not worth an hour of your time and you do not want to be known as the graduate student who goes to events only to eat. Absolutely do not take food home with you unless someone insists. While it is frugal, you will get a reputation from doing this often. Especially if there are "free leftovers" and you take more than one share and leave not enough for other hungry grad students.
* Thirft stores buy your clothing in a thirft store that's in a fancy neighborhood. You can always find things that are basically new and really good quality. Sometimes these items might not be in your size, that's when you flip them on ebay. Apps like Poshmark and Mercari are also great for buying second hand clothing, but are more expensive than thift stores. While you're at it buy your kitchen items and home decor there as well.
* Avoid time consuming life hacks like couponing, apps that give you cash back if you upload your receipt, being a mystery shopper (unless it's a high yield operation), reselling low value items etc. Decide how much your time is worth per hour, and do the math before trying to save on something to see if it's really worth it.
* Milk travel benefits for all they're worth Know what your credit card/airline benefits are before you ever have to use them. Is your flight delayed more than 6 hours? Go on a shopping spree- you're credit card/airline will reimburse you for expenses for "necessities" within a limit that you should have memorized. This is how I buy all of my makeup. Same thing if your bag is delayed- go buy some new clothes and toiletries. Buy the nice kind!
* That's all I've got for now. I hope this can help someone and if not, it was fun to write for me. Good luck with your degrees!