Bring warm clothes if you go in winter. When we arrived in Thimphu at about 21:00 (it was in december)it was about -3C and during night it must have been -5C or colder. At daytime it was just about 10C or less. The air was sharp and cold. Thimphu is about 2400 meters above sealevel. Clothing also depend on where you go as there is big difference between the valleys and the high mountains.
Don't take to much with you - sometimes the buises are awfully crowded. But: Never forget a handlamp !!! Electricity break down nearlly every evening ( and sometimes for hours and more than one time ! ) For Hotel accomodation you will not have to take a sleeping bag with you.
Depends on the time. I've been there in October and it was warm enough to hang around in T-Shirt. Bumthang region is very windy and although in Paro, there is a strong wind at the afternoon. Not really mountain- boots are necessary if you are not exoecting to hike longer.
Bathrooms are mostly o.k. (but think about: Even if you don't feel like - you are in asia ! )but sometimes you will like to wear sandals under the shower and use your own towel...
Take everything and twice times the films you are especting to need ! You will need it - especially you are travelling for the tsechus. All people are like very much, when you take a picture of them and it is nearly unpossible to be alone on a picture !!!
If you do not go on a trekking it is possible to travel with a suitcase. Otherwise a backbag and soft bags are handier.
Good walking or trekking shoes, warm cloths, a good jacket against wind and rain is essential. If you have forgotten something - there are more and more stores selling mountain gear. The main travel season autumn. It is usually dry with fresh temperatures - a goretex jacket against wind and rain is a good thing to take along. If you travel to the East you drive up to almost 4000m (12000ft) altitude - warm cloths are a must.
Medical services are not well estabished in Bhutan - if you regulary need medication you must take them along - a good equiped travel pharmacy is advicable
if you go to ruaral parts better take a torch with you - power cuts can occure