um... one more post ... don't forget to level your picnic table. If using an outside cooking device on the picnic table, there's nothing worse than eggs and pancakes sliding off, or stuff sliding off your dinner plate.
Right now we are camped at Summit Lake State Park near New Castle, Indiana. I currently have 3 of those smaller 2x4's under one picnic table leg, 2 under another and 1 under the third. The 4th is on the ground to get the table relatively close to level. Lumber comes in real handy for lots of things.
I also cut a sheet of left over plywood, 1/4 inch into 2x4 inch pieces. I then painted them with Rust-o-lium black so they would be protected from grease and such, and use them under the electric griddle or camp stove on the picnic table when the table does not get perfectly level. Putting these under the flat griddle, and I can get the griddle almost perfect level, both directions all the time. They are priceless! I've found multiple purposes for them too. I think I have about 20 of them, I carry them in a plastic zip lock bag.