I have a small tool box with the tools necessary for most repairs I take with me. Also included are disposable gloves, big trash bags to lay on (keeps the oil off), wire cutters/scissors for electrical parts removal, hand cleaner, paper towels for hand and parts cleaning, hat for the sun, special junk yard shoes, and other implements of distruction. If they have wheeled (grocery) carts, grab one.
"Pick-N-Pull" yards are a great place to learn how to remove and replace parts before you try at home!
There is usually a price list, so ask first. Not all yards charge the same price for the same parts, a complete door may be the same price as the window alone.
Good luck and have fun!
Mike