Figure out which grocery stores nearby your home have free samples (usually around noon) and be sure to show up for the samples. Walk around the store twice or so to get a decent amount of samples.
Find the local food bank in your neighbourhood. Some post secondary institutions will also have a food bank that you just need to show up and grab a few items off the shelf and never have to sign up for anything.
Go for a visit to your parents and then make your way through your relatives. Go for lunch and maybe they’ll also let you stay for dinner as well.
After a visit to your local library, figure out which berries are edible and go to a local park to see what you can get (this is more a regional thing as some parks may not have berry bushes).
Find out when your school has pancake breakfasts or special events, it’s generally a lot of food for very low cost (especially if you buy a ticket to the event ahead of time).
Only buy vegetables and fruit when it’s in season, it’ll be less expensive and will generally taste better than when they’re out of season.
Also for vegetables and fruit, only buy local. The price difference between imported produce and local is usually quite a bit due to transportation and custom costs.
At the beginning of the school year, some post secondary institutions have back-to-school fairs where there are plenty of freebies such as food, drinks and other things that you might need (ie. pens, laundry bags, notebooks).