open food packages for use on pesach

Question

Is it o.k. to use packages that were open before passover that contain items which can be used for passover? for example, a large container of Oil which is poured into a smaller one for year round use. or a large size of mayo or crisco which is scooped out into a smaller container. also, can an open bag of of walnuts( or other similar dry items) be used if it was also poured out.