Declining party invitation

I normally tell them upfront that I will not be able to attend with REAL reason instead of "oh i have other plans" (technically a lie unless you create a plan for that day :) ). Just let them know that there will not be much in the party for you and if they still want you to come back from party starving, sure you can come.

I have found local people very accommodating on these issues. Couple of times, they actually put the fish on menu just for us other times, I just told them the reason for not coming.