Arsenal (trompos you have) - I think is very important to have a varieaty of trompos, different brands, models and sizes, both fixed tip and bearing, It helps me progress with my play
Aditamientos (accessories) - defenetly string, different strings, thickness and lenght, plus a new sting is always good, I also enjoy the aro (ring) with my play, some people like baby powder (for dry hands), but i prefer this cheap bar of soap that really dries my hands
Herramientas (tools) - I agree with ta0, electical tape