Giffgaff is good.
£25 for always on data which means it is unlimited upto 40gb then it drops to 384kbps from 8am to midnight which is still enough for gaming/streaming.
Also as it’s not a contract you cant be charged any extra you just buy it month to month they don’t tie you down.
Three may offer a better service (I think) but they tie you down to a contract.
Only other advice is with food buy in advance. Because MSA prices are completely crazy. I think if you have to buy in MSA’s go for Greggs or Mcdonalds as I THINK their prices are the same as their regular shops on the high street. (I may be wrong).