Y inventory can hold 1000. So think like, 500 Rubber. 333 of one of three meth ingredients or like 111 I think is the number for all three.
One of my large crates has 4 mk-1's 3 mk18's, 2 katibas, some random pistols, maybe an sdar here and there, and it also holds a few loadouts, csats fatigues, vest, etcc....