Tough one. How about … gems (the old standby), cell phones, iPads, SIM cards, incandescent light bulbs, toolboxes, running shoes …
Running shoes, heh… If you are able to stay in and defend your hopefully coastal harbor-sited bunker I would nominate fuel (diesel and petrol) and two sizes of efficient generators (like the small Honda petrol units, and diesel standby generators). If you are patient you can probably trade a generator for a suitable ship (for which you will need the diesel).
Next, how are you going to keep your pre-doomsday-contracted special forces commando team happy? Without them you won’t have anything left to trade.
Novelist William R. Forstchen explored a plausible future history in which only the running shoes (and my list) would be useful. The book One Second After will stimulate thinking about how to prepare for EOW (end of world scenarios). Forstchen’s imagined world is SE USA subsequent to an EMP attack that wipes out all US and Japanese technology. Which reminds me – you will also want to store a 1960s vintage 1.5 ton pickup truck – the pre electronics model. And what are you going to eat after month six?