- Spread Shot and Smoke Bomb should be your first purchases. They're useful in almost every fight.
- Chaser is a bit of a trap; it's useful against some evasive enemies, but the lowered damage is rarely worth it, and it can get confused by minions and breakable objects in some fights. It's usually worth learning how to aim with a stronger weapon if you can.
- There are hidden coins in the overworld, not just in the run'n'gun stages. They're usually very well-hidden or given by NPCs for completing their requests. Keep an eye out for them.