With what I've read it was normal in the 16th century to offer your guest some sort of gift when they came to a wedding, especially in Italy and France (in France called: bonbonniere). It was a combination of a sign of gratitude and a way to share the couple's fortune with their guests. Mostly the gift of five Jordan almonds are mentioned. Each of the almonds would represent wellwishes: health, welth, fertility, longevivity and happiness.
These gifts of almonds were used by the upper class of the medieval times, along with other exclusive confectionary. Obviously this would make a fine favor for a medieval themed wedding.
Edible favors in general are a good idea for this kind of theme. You can make or buy jam, mead, mustard and honey, or maybe include a genuine medieval recipe that your guests can try out at home. It can also be things like spices, herbs or salt, that had great value in medieval times. Chocolate hadn't arrived in Europe from South America at the time, so sorry guys - no wonderful chokolate favors.
|Honey was the sugar of the Middle Ages|
|Salt was both for seasoning and conservation|
|Jam made from berries tasted as good on bread then as it does now|
|If you have a wax seal - then seal the gift|
|Coins may make a memorable favor|
|A seed favor can be done easily and rahter cheap|