I've just got back from hols, much jealousy! However, hopefully I can answer your q's.
My midwife advised against tablets of any sort - including hayfever and travel sickness. I therefore avoided these but you may want to check with your own midwife in case s/he says any different.
I used an insect repellant that is designed for children (got it from Boots in a spray can). I applied it stood on the balcony and held my breath whilst spraying it on so I wasn't breathing it in, just to be on the safe side! I didn't use a lot but it was sufficient to keep the mossies off (mostly). I can't say whether it's safe or not but that's what I did and I seemed fine.
Use a higher sun cream than usual and use plenty of it - I'm normally fine with factor 20ish but I used 30 this time and whilst mostly ok still have some blotches/burn. Skin seems really sensitive when preggo.
I'd also recommend avoiding ice in your drinks - I had a slightly dodgy tummy for a day or two and once I stopped having ice it cleared up almost instantly. I guess that could go for anyone and not just in pregnancy but it did help me feel better. Stay hydrated with plenty of bottled water also if you're off somewhere warm, I found myself overheating quite easily. Finally, stay cautious and wear some attractive flight socks on the plane to help prevent DVT and drink loads whilst on the flight.
Ooh yes, and if you're staying in a hotel with a lovely breakfast buffet, it's a struggle but avoid the meat and cheese etc that's been sitting around and stick to safer options. I had quite a lot of fruit, yoghurt, bread, small American pancakes etc at brekkie which was definitely more than enough...!
Enjoy your hols