The "bookmark" feature (next to the star in the web UI) may be the least loved and mentioned feature in Mastodon, but it's darn useful.

1) Hm, I might want to read this later. -> Bookmark

2) What a great picture! -> Bookmark and Fav and Boost!!11

3) Do I want to follow this account? Let me take a look later. -> Bookmark

4) I should boost this again sometime. -> Bookmark

Search (somewhat deliberately) sucks, making bookmarking essential to find stuff again. Use it liberally. :)

@eloquence

Also for your own stuff, the auto delete feature lets you set it to not delete anything you bookmarked. You can also do the same for stuff you boost or fav, so lot of flexibility there.