Converting over to WFP the thought of kit breaking down or parts needed was always a thought in the back of my mind. As time goes on you'll collect parts you may need at a later date, such as pumps etc, but fittings is always something I knew would be needed, it isnt expensive to collect a few spares.
I got 2 spare batteries, 2 spare pumps, plenty of pipe-work and a toolbox of spare fittings.
Most engineering outlets sell rectus parts, pop down and buy a handful, if not get 20 quid of spares from Gardiners, it'll give you piece of mind and enable you to carry on working when you find out you need something instead of losing 2 days in earnings.