1. Remove the part you need to replace at home. Take it and the tools you used with you.
2. Take additional tools in case you find anything else of interest. These can be left in your car as you want to avoid carrying tools around the yard or risk leaving them there.
3. Take your work clothes, boiler suit, and an old rug, sheet, or carpet. Removing the part may involve getting down and dirty under the car.
4. When you remove the part from the car in the junkyard, keep all the fasteners – nuts, bolts, washers, etc. You will certainly need these to fit the part to your vehicle.
5. Take some penetration oil to help you remove any stuck parts. If you forget, take a bit of brake fluid from one of the junkers.