Effect > Leveler
Effect > Compressor
Effect > Compress Dynamics (Chris's Compressor -- available separately.)
They will all help. Leveler is a Brute Force squasher that makes no effort to sound good. You can make Jet Pilot Voices with this.
Compressor is an arithmetic processor that changes volume as the show loudness goes up. It can sound good if you're careful.
..Is musical. It was designed to increase the overall volume, even out the variations, and sound really good.