A cheaper side item could be sauces..you get more bang for your buck per gallon as side items. Kraut is something you want to offer. Most Costco, sam’s BJ’s or HG stores sell it for under 7 dollars for a gallon. If nothing else don’t use the .25 get the 16oz can put half of it in a plastic container and the other in 1/3 pan..there tiny…and be perfect. I don’t know how you run your cart..but mine is set up running off of two marine batteries..as I live in Florida and it’s hot as hell..and half my business I plan to do at night. But one of the things you could do when you got some money is get a power inverter..I got one that is 2000 watts continuous and I can run a little Emerson micro that is 600 watts..I can use that micro all day sitting on my cart..I use it to reheat items all the time..takes about 40 seconds instead of 20 seconds with my 1,200 watt home micro. But it’s worth the investment if your going to offer some things that you might only get one or two request for…plus heating up water faster or squeeze bottles and I love my set up cause I can run neon signs and rope lights to stand out at night.
Thats my 2 cents…but your doing pretty good I think if your making close to 80 a day for 3.5 hours…keep fine tuning your system.