We started using large pretzel jars a few years ago. The in-laws like to buy in bulk and brought a bunch of empties over one day to see if we could use them. Ok...truth is they brought them over for hubby to use in the garage for tool parts and I snagged them....but I digress. I used those for feed for a long time, then I started saving other jars. I save any plastic food jar with a screw on lid. Snap on lids can be popped off by chickens. Don't ask how I know this. lol I use them for grit, scratch, chick feed, oyster shell etc. Anything you might need in the coop....I have it in a food jar.
The important thing to remember when saving jars is to only use food containers. Containers purchased with cosmetic or cleaning products in them may leach out chemicals even after they're cleaned. I honestly don't know how much of a problem it can cause, but I'm not taking chances! I clean them out with regular water and dish soap, then air dry them completely before filling. I've been able to cut a lot of time off my chicken chores by having what I need on hand in each coop. As a bonus, every jar I reuse is one less thing that ends up in the landfill!