If done correctly, you can fit 4 tomato plants, 8 peppers, 1 zucchini, and 1 crookneck squash comfortably in that box.

EG

The lady at the nursery never read SFG, apparently!
To expand on EG's comment and answer your original question: assuming your long side runs north-south and can be trellised...I would do 4 tomatoes on the trellises, as well as 1 zucchini and 1 crookneck squash on the trellis (they will all need to be tied as none are natural climbers for the most part). You can either leave about 2 square feet for each of the squashes, or you could plant them each one to a SF which I believe is the default spacing for a SFG? I personally would put one at either end of the box so some foliage can spill out over the sides and be pretty. Then the middle 4 squares can each have a tomato, trellised of course. Next up, you can put in 8 pepper plants. They get large so they each need 1 square foot.
Guess what though? You have plenty of room (half the bed!) left!! You could do herbs, lettuces, radishes, carrots, etc. Generally, of course, you will want to go down in size as you move toward the south side of the bed--so, leaf lettuces, radishes and carrots (which are generally 16 per square) in front of the herbs which are usually 1 or 2 per square.

Here's a sample layout:
Trellis: Zucchini-[z]-Tomato--Tomato--Tomato--Tomato--Squash-[s]
Pepper--Pepper--Pepper--Pepper--Pepper--Pepper--Pepper--Pepper
Herbs---Herbs---Herbs--Herbs---Herbs---Herbs--Herbs---Herbs
Leaf Let-Leaf Let-Leaf Let-Romaine-Romaine-Leaf Let-Leaf Let-Leaf Let
Carrot--Carrot--Radish--Carrot--Carrot--Radish--Carrot--Carrot