I should put this in the "Basics of Basics" of panel alignment. I was at work yesterday and was reminded of how wheel alignment shims are so useful.

Instead of (or along with) using fender shims to shim fenders, decklids, and hoods you can use front suspension alignment shims. They come in many different forms than fender shims. First off, they have MUCH thinner ones, down to a 1/32"! So, you can really dail in something to perfection.
They also make them with little "tails" that form a handle for easier handling in those hard to reach areas.

These shims are available in most parts stores.

Great tip, I've used them for years. Have a small divided box with an assortment. It's amazing how many times I dig into the box even when working on new cars.