Bring back John Brebbia and Jakob Junis
For the most part, stocking up on bullpen arms will never lead the headlines. Sure, Josh Hader is available in free agency and when he signs, it will be big news as he is probably going to get north of $20 million a year, but he is an exception to the rule. However, the Giants do need to build their relief corps back up and one way they need to do that is to bring back both John Brebbia and Jakob Junis.
Are Brebbia and Junis high octane arms that will mow through batters in the ninth inning? No, but the Giants have Camilo Doval and the Rogers boys for that. What the Giants need, in addition to adding a big name this offseason somewhere on the roster, is to add quality bullpen depth and both Brebbia and Junis fit the bill and it doesn't hurt that San Francisco is familiar with both of them.
Brebbia misses bats, generally throws a lot of strikes, and is usually a hard guy to barrel up although he struggled a bit with the latter last season. Junis' slider is an absolute weapon from the right side and grades out very well basically everywhere except when it comes to the results of throwing his fastball too much.
Assuming that there are no long-term concerns with Brebbia's lat injury he suffered last year or Junis' late season neck issue, these are both guys the Giants need to bring back. Neither should cost much and getting the bullpen sorted out will free the Giants to do what they need to elsewhere on the roster.