Greetings!
As one of the cheapest, most depressing career people I know, here are a few things I do.
1) Live in a cheap place -- all your friends will mock you. Ignore them. @Elizabeth Colegrove, one of my RE blog heros lives on a boat atm to save money. As a past boat-dweller, kudos to her.
2) Eat cheap food (as you mentioned) I don't follow this because I'm 50% yuppy, but I have in the past. You don't even need to cook. There are a good amount of affordable pre-made options.
3) Value your time -- uber / lyft could be a time sink. What other things could make you more money in the long run? Educating yourself more?
4) Never feel limited, always think of the alternatives. I sometimes fall into the trap of thinking there is only one way to solve a problem, but money is not always the answer. Think of bartering via talking to everyone you know. Maybe you can trade your services for someone else's.
5) Instead of simply a mindset of saving, consider a mindset of making more money (as some above mentioned).
If it wasn't almost 3AM, I'd post more, but hopefully something up there resonates.
Best,
~Alice