well, our band-practise place has hot a bit pf humidity..our drummers drums are always there and they normal.but how dose it efect amps, cables, pedals?
Depends really, if it's very humid then some of the moisture in the air could negatively affect the amp but nothing too serious, just keep them off the floor and throw a blanket over them when you're not practicing.
Moisture is harder on paper speakers then it is anything.
If you live in a very humid climate that also has a lot of seawater in the air then you may have corrosion of copper traces over long periods of time. Chances are the amp will break because of something else before this corrosion causes any problems. This will literally take years.
life is hard in general, everything is hard on amps, it is impossible to totally protect them unless you keep it in a vacuum sealed environment. that being said, humidity is particularly hard on handwired amps with turret boards. most pcb amps are much more resistant to humidity.