As a European, some tips:
First money:
Discover is distinctly American, we normally use Visa over here. I'm not saying discover isn't accepted anywhere, but I've never seen one so I wouldn't like to guarantee it.
Check the automatic foreign exchange rate on the card, and make sure it's not awful. Otherwise it's not worth using abroad.
Don't use the airport currency change service, the rate on that is awful.
Check you can use the card to withdraw cash from euro cash points without an insane fee. Some places only take cash, so you're going to want some, but some foreign cards charge a fortune for foreign currency withdrawal.
Make sure you roughly know the exchange rate so you don't get ripped off and pay €20 for something only worth $2. It happens.
On another topic:
Our mains voltage is much higher than the US, don't think a simple socket adapter is safe without checking your devices can accept 230 volts. Otherwise when plugged in with a socket adapter they'll explode! You can get transforming adapters or even full inverters that will also change the AC frequency, but they are progressively more expensive and a waste of money if your devices take 230V / 50 hz happily.
Bring a multi-socket with you! Much cheaper than multiple single-socket adapters, and very useful if your hotel room is stingy on sockets. Make sure it's a good quality one, given the higher voltage.
If you can get an actual European USB/phone adapter for charging devices, it's far safer than using a socket adapter. Consider getting a cheap European battery charger and some rechargeable batteries if you have any battery devices.
I don't know Germany, but certainly bring a half-decent camera with plenty of storage, I'm sure there will be lots of photo opportunities.
Don't be afraid to ask total strangers if they will take a photo of you, we're mostly friendly.
A lot of Europeans speak English as their second language, sometimes extremely fluently.
Most major places will have a "tourist information" building, which will have leaflets about local attractions (often with discount vouchers) and maps, and sometimes toilets (useful!)
Edit: make sure your healthcare covers you in Europe! That said, the UK especially tends to forget to bill foreigners, because we get free treatment ourselves.