I currently grow herbs and vegetables in a 4 foot by 8 foot raised bed with a height of about 12 inches. We used untreated pine, which will eventually rot and have to be replaced one day, but I didn't want to use anything that had been treated with chemicals. Below is what I've found works best in a raised bed the size we built. This may give you ideas for your own kitchen garden.
Thyme: in a corner
Oregano: in another corner
Chives: along the front spaced at least 18 inches apart
Sage: in the back left hand corner
Cucumbers & Green beans
Both of these are grown in front of a piece of sturdy metal fencing in the middle back of the bed (see picture below) to grow up instead of spreading out.
Tomatoes: 2 to 3 plants grown in the back opposite the cucumbers and beans. It's important to stake the tomatoes to keep them from sprawling and taking up too much room.
This leaves the center of the raised bed open, plus the space between the chives. I alternate the following herbs and vegetables:
Nasturtium (with the chives)
I add color to the garden with nasturtiums, which are pretty and edible. Calendula is another flower that doubles as an herb. Both can be used in salads, garnish or herbal vinegar.
When looking for vegetables, herbs or flowers for smaller kitchen gardens try to choose varieties that are described as "space saving", "dwarf" or "compact".
Starting with the basics will give you a chance to get a feel for how much work and time the garden will involve. Keep track of what grows well and what tastes the best. This will help you decide how much to expand next year.
On OFL we have an article on growing and cooking with chives: