I'd love to do tickets as invitations, that's a great idea. suitcases as party bags is a bit out of my budget though, sadly - I may get some storage suitcases for 'styling' the house, which DS can then use for storage afterwards!
not sure about meals on trays - I thought maybe some foil trays from the 99p shop with a sandwich, some pretzels, grapes, and a fruitshoot type of drink <awaits banishment from MN for such an idea> then popcorn/crisps/cookies on the table for them to help themselves.
I thought we'd do 2 or 3 party games - pass the parcel (have a toy plane from 99p shop as a prize!), paper plane throwing game (cut holes in large box, give child paper planes to throw through them!), and maybe pin the propellor on the plane if I can be arsed! need to keep costs relatively low, but that all sounds feasible on a budget, I think?