No we don't keep everything. Pictures etc that can be placed on the fridge are done so for a week or two and then replaced with the newer ones. When I take them off they all go into a large tub that we clear out once every 4-5 months. DD can then pick a set number of things to keep (which stay at the bottom of the tub until next clear out) and I pick a couple which go into her memory box. Same goes with DS.

As for workbooks etc that come home at the end of the year, truthfully I only keep them for a year or so until they are replaced by the newer ones. In kindy and pre-primary DD and DS came home with a large "portfolio" of all their best work done in class and I have kept those and do intend on keeping them. They are stored at the top of their wardrobes laid flat so other things can go on top.