My kid is really into knights and castles and stuff, so last year we had a 'knight party' where we served [as much as practical] medieval European dishes. It was a blast!
Some of the most helpful books we used in planning were :
"A Medieval Feast" by Aliki [picture book]
"A Medieval Home Companion" by Tania Bayard
One thing that I really liked was the heavy use of herbs for flavoring. Also, the use of flatbread 'trenchers' as plates is sensible; I guess it's kind of like an ancestor to the sandwich.