if you're going bbq, add some rissoles in there (maybe go 50/50 with the snags) - they always go down a treat. marinated chicken on the bbq is also a decent option - you can get breast fillets and marinade them (buy the bottles - easy!) and do that instead of some of your bbq chicken. means you have both hot and cold chook

roast spud - depends on how you are cooking them - if you're doing baked spuds (like the ones in foil), i'd say 1.5 per adult - some will eat two, some only one. if you're doing them this wake, make sure you have cheese and sourcream or something for them. if you're doing the frozen ones we cheat with, just have a few bags in the freezer - if you have a deep fryer, you can fry them up, drain them - only takes a few minutes - and you can do more if it looks like you're running out. if you cook them in the oven or whatever, you can cook a bit more than you think you need (for our dinner of 11 people, we probably do 1.5 bags if we do it this way) - you can always eat them cold (or reheat) at tea time

prawns - you're looking at quarter of a kilo of prawns each person - do you really need that much?

bbq chooks - get them to cut them into eighths at the shop - saves you work!

bread rolls should be heap - just maybe have a loaf of bread just in case - you can always freeze it for yourselves later.

salad is prolly fairly simple - maybe a salad platter or tossed salad (tom, cucumber, lettuce, cheese, boiled egg),maybe do the platter up with the chicken on it (if you're looking for spesh presentation). those 1kg tubs of premade salad might not be enough if you have a pig like my bro!

alcohol - tell them to BYO!