This is my 2nd year doing the farmers market. I have done several different ones. This year, we're doing 3 markets (2 weekly ones and 1 monthly one).
My advice is this: Do alot of things meant to be like groceries...but also do some individual things.
I make a dozen cookies and put them in a gallon-size freezer bag with a 10" square cake board (from Decopac). People love the packaging because they can fit them in the freezer and they're more visible.
I also do individual cookies...but I do giant ones. They are about 5-6 inches in diameter and I put them in a ziploc sandwich bag. People love them.
Cake only sells in individual little cakes...at least in my area.
muffins...well, the only time I ever sold a good amount of muffins was when I made several kinda and individually wrapped them then separated by baskets and let them choose what kinds they wanted. It was too much of a bother so I only did it once.
If you know how to make bread, it sells like hotcakes at the markets! My mom makes bread and I make pastries so that works well for us.
Pies usually sell pretty well...just start with a few the first week and see how they sell before trying to make too many.
Of course, you'll have to just experiment with what people like because it depends on where you live and really, what market it is. What sells at one market won't sell at another, even if they're very close.
Make it all look abundant! If you don't have much, people won't be interested in looking. The farmers market is about abundance. It's amazing how much more one veggie vendor will sell than another just because he's got alot more things...
Think vertically. Don't just lay it all out on a table. Get some shelves and have some things on the shelves and others on the table. We use white wire shelves and we can take them down as things sell.
Transporting the goods...Have you thought about how you're getting it all there? Boxes are fine for a few things but what I've found to be wonderful are those plastic roll-away bins meant for under the bed. They're not too tall so they don't take up too much space for what you're putting in and they will stack in the back of the van (or truck if that's what you have).
Protect your stuff from the sunlight, especially cakes if you have them. We have these banners that we clip to the canopy tp shade if the sun shines in. Too much sun will make things condense inside and it's gross-looking.
Hope this helps