Getting sick at WDW is the worst - been there, done that, called Mousekeeping at 12:00 am to bring me clean linens after someone threw up, got the t-shirt.
So yeah, mini-pharmacy comes along every time: cold meds, tummy meds, pain killers, NSAIDs, etc. I'm a big fan of 25 mg of Benadryl and 600 mg of ibuprofen before bed. Keeps the achy legs to a dull roar and I am down for the count. No worries about weird bed, etc.
Toiletries are an entirely different matter! The last two times I have gone down with the intention of buying shampoo/conditioner/body wash when we get there. We typically have access to a car one way or another at Disney and it's a huge time saver when I'm trying to get everything prepped at home. Don't have time or energy for the last Target run? We'll go when we get there! Personally, I find that my scent memory is very strong and I like having new products that remind me of vacation when I get home. Also, I love finding products that I can't get locally. Ocean Potion sunscreen anyone?
We almost always fly down to Disney on Southwest so having to check a bag with all the liquids isn't a concern on our way home.