I am a prepper by nature!
I have a decent first aid kit that lives in my rucksack/day bag for went out and about (I have larger ones in each car and the house too). This comes with me on holiday, I check it before I leave and ensure it has plasters etc. I keep a small bottle of hand sanitiser in here too. We take a tube of glucose tablets and oral rehydration tablets too as we are all prone to not drinking enough and needing a hand in hot weather. My partner is a fly magnet so we take insect repellent and bite creams with us too.
At home each car has a little box with one strip of paracetamol, ibuprofen, antihistamines and diarrhoea relief tablets. One of these gets packed when we go away, with original boxes flat packed. It covers the odd headache etc, if we need more, we go to a pharmacy. The car with the children in has a bottle of Calpol, ibuprofen and antihistamines in. I bring a bottle of Calpol and ibuprofen with us. We have prescription medication also so I add these into a bag/box with the above along with dosset boxes. Once we get to other side the meds get put in the boxes.
Toiletries - a new toothpaste, a new shampoo bar for me and my daughter. Both can be used as a soap as well. We take a bottle of my daughters conditioner. We have a new deodorant for both of us.
Suncream - one large bottle for at the place we are staying and a smaller one to go in the day bag. My daughter is prone to dry skin so I take a new tube of aqueous cream with us that does as a moisturiser/aftersun also.
The first thing I do when going through the list of things we need is to see what can be used for multiple purposes. At home I might use different conditioner to my daughter but hers does just fine and we aren't going to use a whole bottle in the time we are away. I never bother taking shower gel but buy solid shampoos that can be used as soap too. Also the bars take up so much less room. Moisturiser, I have a preferred moisturiser and it's useful to have aftersun in case of burning and my daughter has dry skin. I could take all 3 products or I could stick with her cream which I know does a good enough job of the other things. Meds wise, if I was tight on space I would only take ibuprofen and not the paracetamol but usually the space is fine. It's mostly the adults that struggle with seasonal allergies, eldest daughter does a little bit but she's able to swallow tablets and we can cut the adult one in half should she need.
It sounds excessive except we have on various different holidays used /needed everything listed here and it has always been much more convenient to go to the bathroom where we are staying to get something than head out to the shop/pharmacy. I don't buy things separately though it's things I regularly carry all year round. My first aid kit has been used dozens of times on the school run!