Sharp things and nasty chemicals are often thrown away as well as food, so Freegans need to make sure they wear protective clothes.
Newsround sent Gavin to meet Freegans Paul and Alan, and while he didn't climb into any bins with them, he did take a look at what they found.
They filled 10 bags full of food, from pasta to potatoes and even found some flowers!
Shop's view of Freegans
They searched a bin near that belonged to a Marks and Spencer shop.
We asked the shop's bosses what they thought of Freegans, and they said: "We always make every effort to keep food wastage to an absolute minimum, and have reduced the amount of food wastage by 20% in the last year alone.
"We have a phased approach to any unsold food that is approaching its sell-by-date: firstly we offer it to our customers at reduced prices; then to our staff; and finally we donate food to local and regional charities for distribution.
"However if anything is left we must comply with food safety legislation which states that we dispose of products which have passed their sell-by date securely and safely.
Don't take food from bins
"We have a legal obligation to ensure that certain out-of-date food products (e.g. animal bi-products) cannot re-enter the food chain, which is why food containing these products that cannot be legally sold is placed into secured bins.
"We'd strongly advise members of the public not to take food from any waste bins as consumption of out-of-date food can be unsafe."