Oooh My Favourite topic!
Right, in Calangute at tea time the dairy just down from the fish market (same side) sell samosa's, they put it on a plate for you and mix in two types of sauce! - Stunning! (was 5 rs/- last tie I went, but it's been a while. The same place in Mapusa has a little 'cafe' near the wholesale fruit market, follow the bananas at the bus station (that should make sense to some people!

They do the same samosa's and a glass of stunning sweet lassi, lassi is 15 rs/- (best in Goa IMHA)
Fruit Salad and Ice Cream - Mapusa, near the cinema (need to walk away from the market up the hill (and ask for directions), you should find an area of lots of street vendors seperated by a small road (in the evenings), one of them does fabulous fresh fruit salad and ice cream (huge portion) for 20 Rs/- Also the same place does the best tasting fresh lime soda in Goa.
Noodles, Omlette Sandwiches, curry etc, same place as above
Chicken rolls - On the road near the entrance to the Mapusa Bus Station, best tasting chicken roll with chilli sauce - Yum - 25 Rs/-
Puri - I never know what I'm ordering (I just point), they have these small balls of mashed up potatoe made into small fried flat balls, then then add chopped up onion, broken dry 'stuff, coriander, apple sauce, pea curry stuff (sorry about all the technical jargon), put on a small plate for 15 Rs/- lovely!
Sugar Cane juice - Everywhere - gorgeous, always ask for freshly made as it tastes so much better, I have it with Ice but you might want to hold the ice (personal preference)
Next to one of the slums we work at, just down from "The Mango House", the best fresh samosa, potatoe wada and capsicum 'wada'?, 5 Rs/- Bread 2.5 Rs/- great flavour, piping hot (only in evenings).