My Immersion chiller broke after I left it outside in the winter. I replaced it with a CFC (which I keep inside...) and If it were to break I'd replace it immediately again.
Well, brewstand and kettles - although they are unlikely to "break." Something that "could" break, that I would replace instantly - immersion chiller. To be honest though - almost everything I have bought I consider "essential" and can't think of much that I would not replace.
Transfer pump, gotta agree. I didn't have one for 21 years. Bought one and there is no way I'd do without. Recirculating is a breeze. But the main reason is pumping from the patio to the fermenting room in the basement. No way am I ever carrying carboys up and down those steps again.