Supporting and training vegetables to grow upright, away from the soil surface, takes up less space in the bed.
Vining crops such as peas and pole beans grow nicely on wire-covered A-frame structures. When the produce is ready for harvest, it will be within comfortable reach from either side.
There are two types of tomato plants. Determinate types grow only about 4 feet tall and stop. They don't need a tall trellis. A sturdy wire cage suits them fine. They also do well in containers with attached supports.
Indeterminate types will grow as high as 20 feet if you let them. Make a 6-to-8-foot support for them -- whatever is within maximum reach -- and clip off the tips of the main stems when they reach that height. This promotes subsidiary branching and more production.