In the popular free SWS extensions to reaper (So common everyone expects you to install it ) there are options to 'freeze/bounce to track honoring time selection'. Otherwise, you do a track bounce like usual, but only the time-region you selected gets bounced. Lovely if you got small sections in a track (like octave guitars that kick in only every once in a while).
There are also actions to average an item (_before_ plugins are applied though) to a peak RMS or average RMS level, and if you got the latest 'development' version, there are options for EBU loudness analyzing and normalizing.. Great for A/B-ing, and the RMS options are awesome on rendered/bounced pieces that get sent into Nebula so you go 'into the ballpark' of the 0 VU point of the library. You don't always want to hit at 0 VU of course, so always adjust by ear, but for a quick start its nice.
Actions like this are not in the Reaper interface by default. In the action list you can assign a hotkey to it, or create a toolbar with buttons in it for the actions you use a lot.