I have one toolbox for general plumbing tools, and one just for oil boilers. There are duplicates of a few tools such as screwdrivers in each for convenience. I have a number of tote boxes for other gear - an oil one with oil filters, filter bowls, nozzle box, spare oil lines, parts, vinyl gloves, fire cement, glass rope and adhesive etc etc in it, a plumbing one for other plumbing tools, blowtorch etc, and another one for joinery, drills, plugs, tools etc. I have a third tote box which contains component boxes for solder fittings, compression fittings, push fits, washer kit boxes etc, and more tote boxes for other stuff - waste pipe fittings and traps, wc fittings and spares etc etc. For example if I have a WC job I just grab the WC tote box and the plumbing tote box and normal toolbox but leave the others.