It’s common amongst bands, but increasingly so amongst (big name) DJs to have a “rider”.
A rider is a document outlining the minimal equipment that needs to be present at the venue on the night of the performance.
Be sure the rider is exact, so don’t write a CJ-player, but write:
DJ Booth:
Sufficient space to set up controller (DDJ-SX) in flightcase, dimensions WxDxH
Ability to connect to house PA, balanced XLR or 6.3mm Jack. RCA is allowed if distance DJ Booth <-> PA is less than 6ft
Alternatively:
2x CD-/Mediaplayer:
Pioneer CDJ-900 Nexus
Pioneer CDJ-2000 Nexus
1x Mixer:
Pioneer DJM-900 Nexus
Pioneer DJM-2000 Nexus
Xone:DB4
In either case (controller or mixer/cd-/mediaplayer):
1x DJ monitor speaker. Minimum 10″, biamped, 250W RMS or more. Connection balanced XLR or Jack
Something like that (obviously you put in what it is you want in there). Make the rider part of the deal/contract.
It saves a lot of hassle once you get there and things aren’t what they are supposed to be.