Fresh lettuce has green leaves with no wilted or bruised areas. Signs of overripe lettuce includes discoloration, limp or soggy leaves and an unpleasant odor. A head of romaine or iceberg lettuce will last for seven days in the fridge, while more delicate lettuces will spoil faster.

A ripe onion is hard with dry, papery skin. The roots should be two to three inches long and white in color. Keep an eye out for green spots or leathery areas, which can indicate that the onion is starting to go bad.

Fresh peppers have a firm exterior with bright, glossy coloring. If the pepper starts to wrinkle then they are still fine to cook with but will be less appealing as a raw snack. Peppers that have softened and continue to wrinkle will soon become slimy and inedible.

Ripe sweet potatoes are thick, medium-sized spuds without any bruises or decay. They should also taper at the end. Sweet potatoes that are wrinkly and mushy should be thrown out.

White potatoes should be mostly smooth, firm and free of blemishes. Avoid buying any white potatoes that show signs of bruising, sprouting or shriveling. A green tinge is another sign of over maturity.

Fresh tomatoes are plump with a rich, red color and slight softness. Look out for any cracks, discoloration, sunken areas or other damaged spots on the skin of the tomato. These are all signs that the tomato has gone bad.

A ripe butternut squash should be beige all over with no visible green patches. The skin should be matte, not shiny, and the squash should sound hollow if you tap on it. 

Zucchini should be a dark, solid green color covering the entire vegetable. They should be firm but slightly flexible and 6-8 inches in length. If you're cooking with your zucchini, such as making zucchini bread, it's best to choose one that's a bit softer so you know it is at peak ripeness to use right away.