The three main accessories for the Akai MPC 2500 are:

CD / DVD Expansion Drive CD-M25: 
Add a CD / DVD Rom to your Akai MPC 2500.

Hard Drive Adapter Kit for MPC2500 HDM10:
Add a Hard Drive to your Akai MPC 2500.

MPC 2500 EXM 128 Expansion Memory Upgrade:
Get the most out of your MPC and upgrade your Akai MPC 2500 Memory