Exegesis:

ei oun oude elachiston dunasthe ‘if then you cannot (do) even a very small, or, insignificant thing.’ The reference to what precedes is brought out in “as small a thing as that” (Revised Standard Version). The rendering ‘the smallest thing’ appears to be too emphatic. The clause is conditional in form but inferential in meaning.

peri tōn loipōn ‘about the rest,’ i.e. about physical necessities.

Translation:

If then you …, preferably, ‘since you…,’ ‘thus it is certain that you…,’ cf. the remark on the “if”-clause in 11.20.

As small a thing as that, or, ‘such a small thing,’ ‘such a trifle’ (Javanese).

The rest, or, ‘the other things,’ “anything else” (Phillips).

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.