The best thing you can add to sandy soil is compost.* It will help improve the texture of the soil, increase the water holding ability and add good microbes.* You can buy it in bulk or in bags.* It's usually less expensive in bulk.* Of course adding an organic mulch after you plant will also help.
I did a google for conrbread dressing and there were so many recipes my head was spinning!
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.