My company pays a certain amount for meals with no receipts needed, so if I spend less it is tax free bonus! For dinner I will often go to a grocery store and most have deli counters that have quarter chickens as well as sides of veggies available (or will grab a microwave bag of veggies if my room has a microwave). I can have a good, healthy dinner for under $10 and pocket the “profit” from what the company pays. Plus I HATE eating multiple meals at restaurants. It gets so gross. And it’s faster than a sit down restaurant.
This. Get a flat per-diem if possible, and always, always, always get a hotel room with a fridge. Even if it doesn't have a microwave, with a kettle and an iron you can do quite a bit. (Yes, an iron. With some tin foil this can be your friend.) When I traveled almost 50% with a previous job I would find the nearest grocery/deli/bodega, and stock up on things like yogurt for breakfast.
Other tips: Get one of those wide mouth thermoses. With this you can 1) buy a half carton of eggs, and pour just-off-boiling water over them in the thermos, and get hard boiled eggs. 2) Make oatmeal. 3) Get a smaller container that fits inside, pour hot water around it, and heat up just about anything.
Get some of those collapsible camping bowls, and a portable can opener. Now you can make tuna, egg-salad etc.
If you want to bring your own food, you can, but make sure you research the quarantine rules of where you are going. I've had to throw away things like grapes entering California, and nuts entering the US as well. It often isn't worth it.
If food is allowed, flour tortillas and peanut butter travel really well. Make your own trail mix in advance as well. Read backpacking sites for food suggestions that will travel light and heat up just with boiling water.
Non-food related travel frugality, especially if you are going to be on the road for a while:
Get a travel clothesline, the latex braided kind. My company wouldn't pay for laundry, so having the ability to wash things cut down costs substantially. Get a universal plug for sinks - not every hotel sink can be stopped. Bring a bottle of laundry detergent, and wash away. Ask for extra towels, and roll wet things in the towels and kneel or stand on them before hanging up. Cuts down dry time substantially.
Always carry-on everything, even if your company will pay the extra for checking a bag. If you have to buy sundries and clothes when (not if) your bag is lost, you will always spend more than the airline will give you. Not worth it.
My max was three months on the road without a break, living out of a single carry-on. That was too much, but I made a lot of money on my per-diem that trip.
Get some of those packing cubes and prepare kits, like a food-prep kit, laundry kit etc. Restock as you unpack. That way, when you travel, you can just toss the kits into your carry-on.