For learning new songs and practice between band rehearsals I use my Tascam MP-GT1 MP3 Guitar Trainer. This walkman-sized unit is built to last having an aluminium back and sides and contains a 1Gb memory for storing up to around 240 songs in MP3 format.
Its easy to upload songs and put together a playlist to practice before a gig. The songs can be speeded up & slowed down and the key & tuning can be changed. A guitar tuner and a good selection of digital fx are built-in. I only use the fx on mine if I am playing guitar. As I play bass through it most often I don’t use the fx as it sounds good without needing any for bass. A bass specific version is also available, the MP-BT1, however this was not available when I bought my MP-GT1.
More information is available at tascam.com including specifications, owners manuals and details of similar products.