You can plant one borage plant to attract pollinators. You only need one, because it will self-sow and grow new plants all over. Marigolds add color and some say they repel insect pests.

You might also want some herbs, like basil and parsley if you like to cook. Some of your plants are from different growing seasons. For example, peas, winter squash, lettuce, and kale are cool season plants. Tomatoes, beans, and yellow squash are warm season.

Here is a link that might be useful: What's Growing On?

lgteacher has excellent suggestions. To add a few more possibilities

* nasturtiums--a flower with edible flowers and leaves. Use as a garnish on salads to add a little peppery flavor
* cover crops to build your soil or attract beneficial insects. Buckwheat, clovers, vetch, oats--there are very many possibilities.
* soybeans?

You need to borrow the book 'Square Foot Gardening' by Mel Bartholomew from the library. He has out two. The 'All New Sqaure Foot Garden' features his new method of soil structure and if your beds are already filled with loam and amendments you won't need that volume, but the pictures are in color. Both books, tho, are filled with lots of info on when to start what in your garden. transplanting, companion growing, trellised crops, how many to grow per square. For example squash and zucchini take 9 squares of space for each plant while you can put 9 spinach or bush beans, 16 carrots or radishes or one kale in a square. Peas and pole beans need to be trellised. Anything trellised or any upward growing vines should be planted on the north side of your boxes so as not to shade other crops. Tomatoes can grow in 1 square if you trellis, string or stake them. Cukes would do well in your 2x4.
From what I can see, you won't have enough room for all you want to grow with squash taking up so much space. But if you plant it in a corner so that it can hang over the sides of the bed, you could get away with only 4 squares per squash. And yes, you can grow some things after you pull out the early crop if you know which ones do well in your area. You can even start new fall crops when other early ones have been harvested.
Get thee to a library and read a little more. I recommend: 'Square Foot Gardening' by Mel Bartholomew, 'The New Victory Garden' by Bob Thomson, 'The Garden Primer' by Barbara Damrosch, 'The Vegetable Gardener's Bible' by Edward C Smith. All have something to offer any new gardener. I know you'll enjoy SF Gardening.

Yes but you only need one square to grow zucchini in...been doing it for years. You also can grow bush beans that dont need to be trellised and that could save you some extra squares. You also dont have to plant on the north side if you want to intentionally shade an area of your garden to cool it down-example would be growing lettuce in the dead of summer. If you can keep it cooler, its going to do better....

Thanks for your help!

lgteacher - I'm sorry, I've never heard of a borage plant - is that the name of the plant, or is it a type of plant (like the marigolds)?

ralleia - thanks for the suggestions - I think I read somewhere that nasturtiums were good for pest prevention, so I may add a block of those.

quiltbea - I'm planning on getting those books - I've been reading the sfg book, but apparently missed how much space to allow for yellow summer squash. I'll adjust my plans to account for the larger space requirement. I was planning to put them in one of the 2x4 beds. If I put a plant in each end of a 2x4, would that be enough room (the leaves would be hanging over) or do I need to allow for a bigger bed?

snibb - yes, I was planning to use bush beans - I should have stated that in my op. Thanks for reminding me.

Also, I'm thinking the 4x4 is a suggestion, not a requirement, so I may adjust to fit what I need. Thanks everyone for your help!

Unless my math is wrong you have 32 squares. You should be able to grow everything on your list in there without any problems

As for zukes and squash.......I can only go by the spacing I need for my own squash plants. Mine grow huge and give and give all season long. I don't train them up a trellis.
Putting your zukes and squash in your 2 X 4 may work out fine for you.
Pole beans need trellises and bush beans don't.
When you need more shade, you can always cover the plants with cheesecloth. I drape mine over wire coat hangers stretched into a tent curve shape and clip with clothespins.
Go for it.

The All New Square Foot Gardening book recommends planting summer squash bush type one plant per nine square feet and vine type 1 per 2 square feet. Buy planting one bush type at the end of the bed you probably can get away with 4 square feet with a lot of overhang into the rows.