Gardeners have developed many different strategies to maximize their yields from small spaces. For starters, think vertical! You can train "indeterminate" (climbing) tomato varieties and pole beans to grow up strings or trellises--perhaps along the back edge of your raised bed, especially if it abuts a wall to which you can attach your trellis.

Winter squash can climb on strong vertical supports, too, though if you have space outside the bed, you could plant your squash in a corner and let the vines run out over the ground. [If you want summer squash (zucchini, patty pan, etc.), try one or two plant of one of the dwarf (compact) varieties.

If you do grow vertically, make sure to map the path of the sun and plant accordingly, so your climbing plants don't shade the low-growing ones.

For your lettuces, try growing a mesclun mix (see photo). Scatter the seed fairly thickly across an entire 2-foot area. These mixes grow fast; within about three weeks, you can begin thinning the bed and pinching off the larger leaves for salads.

When choosing which varieties to plant, pay careful attention to the package directions, which should tell you how tall and wide the plants of that variety will grow, how many days to harvest, and the sorts of soil/environmental conditions the variety prefers.

Have you thought about the soil for your raised bed? How will you fertilize your crops? Learn to monitor them for pests and plant diseases? There's a lot to learn! But it's all fun.

Finally, many varieties of each of the crops you mention will grow well in containers (burlap bags, galvanized tubs, 5-gallon pails, plastic tubs, etc.) in case you want to spread out a bit.