What is a good simple hand tool for packing small surfaces of dirt to prepare it for laying concrete? I've seen big pneumatic hammers at large construction sites and was wondering if there is a good manual version of it.
I use a plate tamper. Most of the hardware stores, garden centers, and big box home improvement places around here carry them.
Search for a tool called a "dirt tamper" It's basically a flat retangular metal plate with a slot for a handle.
Contrary to common opinion, you don't need a special tool for every job.
Depends on the size and depth you may get away using a sledge hammer to ram the soil down. If the hole is deep/narrow, a scrap length of timber (lumber) around 4x2 and long enough to reach the bottom is adequate. Use it as is, or like a big nail punch in combination with that sledgehammer.
Put in no more than 1-2 inches (25-50 mm) of soil and pack it down. Don't try compacting thicker layers by hand, you'll just end up with a layer cake of looser and firmer layers.
I might do something like this a couple times a year, and its worked fine for me.