Farmer Survivors

This is cumulative over all runs, because the most weapons you can have is four in a full run. However, you get to choose a new weapon at the start of every run, so you could literally just start five runs and choose a different weapon at the start of each one to unlock this achievement. Otherwise, it's easy enough to do this in the two runs you need to do for the base game and first title update achievements. You'll unavoidably have four different weapons in your first full run of the game, so in your second run, just start with a weapon you haven't used yet and you'll unlock this achievement.

This is cumulative over all runs, because the most weapons you can have is four in a full run. However, you get to choose a new weapon at the start of every run, so you could literally just start five runs and choose a different weapon at the start of each one to unlock this achievement. Otherwise, it's easy enough to do this in the two runs you need to do for the base game and first title update achievements. You'll unavoidably have four different weapons in your first full run of the game, so in your second run, just start with a weapon you haven't used yet and you'll unlock this achievement.