Depending upon your growing Zone, you may be able to produce at least two separate crops of many of these vegatables - especially those that only need 30 to 80 days to maturity. If you start plants early (indoors or a Greenhouse) you will get a jump start on your crops.
In the spring start plants 4 to 6 weeks before your last frost date. Check with your County Cooperative Extension to find that date. When the first crop (in summer) is starting to be picked you can start a second crop, which will mature before your first fall frost date. You can use row covers to protect them from chill if needed.