"I do not have anything now."
Translation:Ich habe jetzt nichts.
There's no simple rule for this, but I'd say "nichts" is an object (o. complement), so it goes to the end, if there is no infite part of the predicate (verb complement) (e.g. "Ich habe damals nichts gehabt"). The remaining complements follow the "TeKaMeLo" rule (http://www.dartmouth.edu/~deutsch/Grammatik/WordOrder/WordOrder.html), that means the temporal complement mostly preceedes all others.
Could it be "Ich habe im Moment nichts"? I know that sounds more like, "I have nothing at the moment." Does jetzt imply that you had something, which is now gone? And if so, does "gerade" also fall more into the former category? Thank you in advance if you are able to answer :)