Really the only consumables for running a tumbler are your abrasives.
These can be ordered individually.
Most commonly they are ordered in a four step kit.
The Small Four Step Kit, Lortone#590-030 $26.95
contains enough abrasive to polish 12 lbs of rock.
The Large Four Step Kit, Lortone#590-032 $99.00
contains enough abrasive to polish up to 25 lbs of stone.
Infrequently but on a occasion the tumbler belts do wear out over time.
We also sell those for $2.50 or $5.00 depending on which size you need.