1. Eliminate any experiences pre-med school unless they are genuinely significant (no one cares if you did Habitat for Humanity for spring break, but they might care if you coordinated and organized volunteers in your community for 2 years).
2. If there are similar entries for your volunteer experiences, lump them together, especially if there were multiple short ones. For instance, if you volunteered in a club providing clinical screening in the community and did a total of 10 different events, you should list that as one category rather than 10 separate events. If you did the same 'job' at two organizations in the same area, you can lump those together as well.
3. If you don't want to talk about it in an interview and it wouldn't look weird to drop it, drop it. Things that would look weird if you dropped: anything that explains a large gap in education or employment. Not like a summer semester, but a regular semester maybe. Things that build upon each other--if you only got into Y lab because you worked in X lab, it would look weird if you took out the experience on X lab.
Otherwise, keep everything. PDs know that a lot of ERAS information is fluff, but it does provide fodder for interviews.