Our in laws lived in Spain when Joseph was born & we took him abroad at 4 months & have taken him abroad 2-3 times per year ever since. As long as you are sensible in the sun with them & make sure they have good sunblock on, a UV bathing suit is good as they cover most of the body, this way only bottoms of legs, arms, neck & face need sun lotion applying. Make sure babies head is covered with a hat & use a parasol to keep the direct sun off them. Depending where you travel abroad (if you decide to) they sell lots of UK baby stuff over there so you don't need to take it with you. For example "Dodots" are the foreign brand name for Pampers, so you can buy wipes & nappies when you get there. The only thing I would definitely take is Formula as brands are very limited abroad. Joseph wasn't a fan of the jars of food abroad, but as we were self catering we just made him food as we did at home & just packed baby rice & porridge in boxes in our suitcase.
You just need to adapt things depending on babies age. A lot of hotels provide welcome packs for babies with nappies, food, formula etc. so you don't need to take it all with you. Travelling in the UK is good as you have all mod cons already here & if you forget something, you can get it when you're there. As everyone else has said, have a break & take baby out of the car seat every 2 hours approximately for a stretch. Most important of all, just enjoy your holiday & your time together as a family x
Sunnyb xxx