Oh yeah, I've never walked into a wedding without having duplicates of everything. You get one chance at it. Not having backups is asking for a disaster. But something like a portrait shoot, you can re shedule if there is an equipment failure.Personally "work" and "one body" don't go together. I learned my lesson at a wedding I was second shooting. The primaries flash started acting up and he had figured "small wedding, I'll go light". Sadly he was Canon and I was Nikon, so I couldn't let him borrow one of mine.
The situation you were in is the reason a lot of wedding photographers will only take on second shooters who shoot the same brand.