You have to pay US federal income and possibly state income taxes even though you'll be living abroad. BUT there are some tax breaks and rules against double taxation that can help avoiding any payment. I.e.: you can write off dutch taxes on your US return.
Don't travel back to the US for more than 35 nights in a single year to get all the tax benefit (make sure you also qualify for your US state's expat tax breaks). This includes any type of travel — work, vacation, through-transit, etc. Do some research on that, I'm sure I'm over simplifying, and it can vary state to state.
Take any cold/flu medication you like with you. they don't have OTC drugs there
Start learning the language right away! Even though you can get by with just English. At least get to the B1 level. It's a great language and it will make life much more enjoyable.
Watching local TV, particularly news shows, in Dutch with subtitles turned on is a great way to improve language skills
Enjoy!
Minor point, but I'm not sure what you mean with the bolded part. Drugstores here sell Tylenol (called paracetamol here, same substance), aspirin as well as ibuprofen and such. Heck, drugstores even sell morning after pills over the counter in this country (15 euros, for who's interested). It's the sedatives and sleeping pills that might be more restricted here.
But of course, I don't know what wonderpills are available in the US for colds?
We stocked up on cold and flu tablets before arrival (you can't get pseudoephedrine here, but you can buy it over the counter in Belgium next door - go figure).
If you have specialist medication, check into how to source it. I take a specialized drug for a stupid auto-immune disease. Costs me $40 a month back in Australia on our health system. I kinda fall through the cracks of the health systems here, and buying it on the open market would be about $2k a year - hence I'm getting scripts filled back in Aus and shipping it across - I'm also still a resident Australian taxpayer.
The other one that took a bit of getting used to for us was Dutch banking. Outside of museums its rare to find places that will take international credit or debit cards. No Pinnen (Dutch debit card)? Tough luck. Try to get your local bank account sorted out on the day you land.
I second the view to getting a bike asap. Cities here are pretty compact - we can get to most things we need by foot or bike. We bought second hand bikes and a decent bike lock - plenty or stolen bike stories. Also got a kiddy seat for out 11 month old kid - he loves it. We are debating about getting a car at the moment - cars are expensive here. If we didn't have the little one, we certainly wouldn't get a car. With the little one, its line-ball for us.
The Dutch wealth tax is difficult if you are in two tax systems. Ignoring a whole lot of fine print, they basically look at your net worth, assume a 4% income from it, and tax it at 30%. They don't tax dividends or capital gains. If you are only exposed to the wealth tax, it works out about the same (compared to Australia at least), expect paid more smoothly. Unfortunately, I don't get any discount on the dividend taxation or the capital gains tax I'd pay back in Aus, so with a ~3m net worth, its basically tax prohibitive to get a job and become a Dutch tax payer. Luckily, my wife is here with the Aus embassy, and we can elect to stay as Aus tax payers (provided we don't get NL jobs). I've been doing a bit of contracting remotely through my AUS business for AUS clients for some pocket money.