Picture of Easy Bike rack
As a broke college student, I try to use my bike as much as possible for transport and such, however groceries can be a challenge when you have to use mad Tetris skills to fit everything into a backpack or suffer with bags hanging off of your handlebars.  I knew I wanted a bike rack that I could attach one of my milk crates to to add some cargo space, but even cheap ones cost upwards of $20 or 30.  Then when I was helping my family clean out our shed I stumbled across the bike seat used by my parents to haul me around when I was a youngling.  I had an idea.

To make this bike rack you will need:
-an old baby bike seat (looking online it seems like most will work for this)
-a small sturdy wire rack (I got mine from an old camping grill but a small microwave oven rack or any sturdy wire rack would work)
-a few zip ties
-some paint if you wanna make it look nice

I apologize I don't have any pictures of the raw materials because I made it a few months ago, but a quick search of google images shows all sorts of baby bike seats that look similar to what I used.