Two suggestions that are valuable additions to any player's gig bag:

Electronic tuner: Take your pick of many under $40, but if your bassist plays a five-string, make sure the tuner can handle a low B -- some can't.
Recommended: Korg GA-1 or GA 30 Guitar/Bass Around $20
If you have more money to spend and want a tuner that can be used onstage, consider the Boss TU-2 Chromatic Tuner and power supply. This tuner has a pedal that takes your signal offline for silent tuning via LEDs. It has the added benefit of acting as power supply for Boss effects. Street cost is about $100.

PlanetWaves Bass ProWinder peg winder: Makes changing strings easy. The winder accommodates "elephant ear" tuning pegs and includes a wire cutter for snipping off excess string length. Less than $10
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"Bass is the foundation of the band." -- William Murderface, Dethklok bassist
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Lakland 55-94; Lakland Skyline Joe Osborn 5; Hofner Icon; OLP Tony Levin Signature 5 String; Stagg EUB; Genz-Genz Shuttle 6.0; Line 6 Lowdown Studio 110; Radial Bassbone