Things that immediately come to mind:

• regularly check for whether your commits need rebasing
• check on what your colleagues do
  • are there (semi-)open meetings that you can attend that benefit (from) you
  • what are upcoming features?
  • have a look at what colleagues are coding and if it isn't obvious what they are doing, ask, this helps keeping a very top level overview and you might even be able to help out if someone e.g. gets sick


• document your changes

Another article that might also be interesting in that context is that one: dev.to/joefuzz/how-do-you-share-kn....
I've answered to that one with a few things that you can probably do when waiting for a review: dev.to/joefuzz/how-do-you-share-kn...