Determine how many watts you are going to need to run whatever it is you are going to run. Look at continuous and peak load needed.
Of course don't forget our friend Ohm...
that is, don't forget to convert the amps to watts to determine what size you will need.
ampsX120v = watts
A modified sign wave inverter should work fine although you may want to look into a pure sign wave one. I too run one in my Jeep, 2000 watts and there hasn't been anything I have hooked to it that hasn't work well from hand tools...cutters, grinders to a microwave or blender. Sometimes though a small incandescent light has to be hooked up to it also in order to load it properly for a particular appliance. But other then one or two items it works for all I need.
Some work better with some appliances then others. Shop around and ask the various manufacturers if their product will work for your particular wants/needs.