In my world, the couple usually just buys the cake. Assuming they're doing a Western-style wedding, that is. But the guests are supposed to bring money for a gift, so it ends up not costing the new couple as much as it would otherwise.

[... it feels a little odd to be discussing wedding traditions, honestly. Until he arrived in Luceti, Gai hadn't thought he would ever have the chance to have a wedding at all.]