Some foods should not be vacuum sealed, as they contain anaerobic bacteria that can grow with little to no oxygen and can be dangerous. Food such as raw mushrooms, garlic, soft cheeses, and freshly cooked or steamed veggies (you must let them cool to room temperature to do that) should not be vacuum-sealed.
Some types of vegetables should be blanched before vacuum sealed, as they can emit a gas that will cause them to spoil. It is a good idea to prep veggies before bagging them.