Every RIF I said I'd never sell, I sold eventually, even the ones I loved , like my TM MK23, Hexagon PPSH-41, TM Breacher, KWA Vz61 (due to fear of eventual expensive failures... Because all airsoft guns break eventually).
At the moment, I can't see me selling my Scorpion Evo or TM G17 Custom (even though I now use a G34).
As for kit, my most valuable item is my ancient Black Bear Airsoft mesh mask. It allows me to play much more aggressively, feeling safe about getting shot in the face. That and my Blackhawk G20 Serpa holster. Love it for quick draws. My KWA speedloader is fairly essential too. So much more robust than the TM version.