Another Year with the Back-Porch Garden

Until we get a house I will just have to continue to make do with my 8' x 8' piece of concrete for a garden.

This year (back to front):
a row of radishes & a row of green onions
Solar Fire tomatoes (heat tolerant... we'll see...)
Husky Cherry Red tomatoes
cantaloupe (this one will definitely surprise me if it works in a pot...)

Any tips/advice to keep a potted garden from drying up and dying? Last year, I didn't have very much success. I thought I'd try again, nevertheless.