I've traveled to Bali eight times spending anywhere from two weeks to a month on each visit. In this day and age of increased volcanism, earthquakes and potential tsunamis one should definitely consider what their exit/survival strategy, if possible, should be. I've always had a very good guide who speaks excellent English and can help navigate any medical or administrative obstacles. Acquiring an international telephone once there is useful as well.
Bali is very hot and humid so make sure to carry extra bottles of water to stay hydrated. I frequently drank a local coconut water called Hydro that they sell in convenience stores. It replaces some lost electrolytes, tastes good, and is much healthier than the ubiquitous technicolor Fanta drinks. The water is also undrinkable and you probably shouldn't brush your teeth with it either. I took some charcoal tablets with me and this time didn't have any upset stomach problems. Along the vitamin replenishment line of thinking it may be good to carry Vitamin C or a good all around multivitamin. Bali's pharmacies or Apoteks are not so nearly well stocked for the many small apothecary items we take for granted so take with you a decent all around stock of what you might possibly need.
Ubud can also lose electrical power at times and on my recent visit it was dark for about two hours. Being a tad cautious I tend to keep extra food stocks and water around at all times. Another note of caution is that Bali sprays lots of pesticides because of fleas, mites, etc., another reason for Vitamin C and detoxing beforehand. In Bali I've been bitten by fleas, not fun, and there are natural versions of flea and mosquito repellents you can take with you. Even worse is the potential problem of mites or scabies type pests due to past overcrowding with mange infected dogs on the island. The first time this happened to me it was incredibly uncomfortable and was probably due to visiting and hanging out in an orphanage I'd been going to. My most recent trip to Bali, having just gotten back a few days ago, I again acquired a mite-type infestation from not considering that cheap massages on the beach or a masseuse's hands and wrists may be infected. I spent much of my time trying to find a remedy and literally nothing was available because I think the Balinese are more used to this kind of thing than we are. Nothing sucks the life and enjoyment out of a trip more than knowing you have something crawling around under your skin making you itch. I have noticed the Balinese often do scratch behind their ears and around their eyes and noses which can be a sign of mite infection. Oh, and check the hotel mattresses for bedbugs, because those came home on one trip with me and it was hell getting rid of them. This trip I looked and all the mattresses looked new and in good condition and I usually stay in Balinese bungalow type places. Again they spray lots to avoid these pest problems so know that most places have been doused in pesticides.
The area of Kuta, except for the beach and surfing during the day, is best to be avoided especially at night. Very dodgy and has a dark feeling which is difficult to shake. Watch out for massages in general as I think that many of the "trained" masseurs use a type of kundalini massage energy which gives you this pleasant ecstatic like feeling. Again, not something I was expecting nor asked or wanted and it was not stated on the description and then about forty minutes into it is was like whoa what's this. Well, that's probably enough for now. If you have any questions just post and I'll do my best to answer them. Hope I haven't completely horrified you but most likely you wont' encounter as many problems as I have as I have had lots of contact with locals, small villages and some of the poorer areas. Hope this helps.