The deponent verbs utor (use, avail oneself of), fruor (enjoy), fungor (perform), potior (take possession of), vescor (feed on) and some of their compounds take the ablative.

ut perinde nostris rebus ac nos tuis perfruaris [I.4]

igitur ut te non decurione solum verum etiam equite Romano perfruamur [I.19]

ut dignitate a me data ... quam modestissime utare [I.19]

This use of the ablative is means, with deponent verbs that imply the middle voice:

utor       "I employ myself by means of" > I use

fruor "I enjoy myself by means of" > I enjoy

fungor "I busy myself with" > I perform

vescor "I feed myself with"  I eat, feed on

potior      "I make myself powerful with" > I get hold of

 

Similarly nitor (rest on, rely on) and the adjective fretus (relying on) take an ablative of means.

nitor "I support myself by means of"

nitebamur ... sententia Meti Modestus [I.5]

Opus est (and sometimes usus est) "there is need of" takes an ablative of means. Opus est: literally "there is work" + the ablative of that by which the work is to be performed.