おか means 'pile' in [来年も仕事があるとは限らないから、ちゃんと貯金しておかなければいけない。] right?

おか is not 'pile' here. It is a conjugation of the auxiliary verb おく.

A verb in te-form + おく means to do the verb in advance, or in preparation for something. So 貯金しておく means to save money in preparation for something, i.e. for the possibility that there will be no work next year. I think this is where the 'while I can' part of the English translation comes from.

I find ちゃんと rather a tricky word. I guess 'diligently' would work here. We can only guess why the translator omitted a translation of this word, but I don't think it really adds anything to the English translation.