Bass string winders. These tools can quickly and easily detune and tighten your bass strings when changing. This can be a surprisingly tedious process and uncomfortable for your hands, and these cheap tools can make the whole thing quite painless- particularly for upright bass.
D'Addario Planet Waves Bass Pro-Winder String Winder and Cutter DP0002B
D'Addario Planet Waves Bass Pro-Winder String Winder and Cutter DP0002B Price: $12.99
Pro 3 in1 Guitar String Peg Winder Cutter Clippers Bridge Pin Puller Bass Suppy
Pro 3 in1 Guitar String Peg Winder Cutter Clippers Bridge Pin Puller Bass Suppy Price: $2.63
D'Addario Planet Waves Bass Guitar String Peg Winder
D'Addario Planet Waves Bass Guitar String Peg Winder Price: $6.99
10 Pack D'Addario Planet Waves Ergonomic Bass Guitar Peg Winder, PWPW1B
10 Pack D'Addario   Planet Waves Ergonomic Bass Guitar Peg Winder,  PWPW1B Price: $62.95
3 in 1 Guitar String Winder Cutter Puller for Guitar Bass Mandolin Ukulele
3 in 1 Guitar String Winder Cutter Puller for Guitar Bass Mandolin Ukulele Price: $19.46