@erik_squires pretty much covered it. The other parts that can dissipate power are inductors, particularly those wound with very thin wire like you often see in less expensive (and some pricier) speakers.
Passive crossover power usage
The last thread about crossovers (good and bad or as is and rebuilt with better components) got me thinking about the power required in watts to run it. Actually heat dissipated by the crossover itself. Seems to me it must be minimal if some of you guys a running systems with crossovers and are using 2-5 watt flea power amps on efficient speakers. Any ideas? Thanks.