Tesco do noodles for like 16p
Tap water is free, hopefully you'll have access to a kettle
As a treat, go to the reduced sections of supermarkets. You can usually pick up ready meals for less than 20p. I got a delicious Tesco's Finest Malaysian chicken curry for 14p a few weeks ago!
I've never been to Falmouth, but it sounds small. Walking is free!