As someone who goes to Germany frequently, but speaks very little German (working on it!), I can offer this:

(Also keep in mind that an overwhelming majority of Germans speak English, so it makes it a bit difficult to be forced in to learning the language while there)

These are pretty basic, but good to have hammered in to your brain:

Danke (schön)/ Bitte - Thanks (Thank you very much) / Please. Note that Bitte can also mean "Pardon?" and "Your welcome" (usually as Bitte schön), and will sometimes be used when you are served food, similar to "bon appetit," though I've mostly heard this in western Germany, less so in the east.

Guten Tag / Hallo / (Guten) Abend / (Guten) Morgan - Good Day / Hello / (Good) Evening / (Good) Morning. I don't think I've heard "Tag" used by itself, but I have most certainly heard Morgan and Abend used by themselves.

Auf Wiedersehen (Good bye) - Honestly, except for getting off airplanes, I don't think I've ever actually heard anyone use this. Granted, it could be because of the company I keep that people are more likely to use tschüss or tschau (both mean "bye" and to an American ear sound kind of like Chews! and Chow!), so I can't really say for certain.

Entschuldigung, sprechen Sie Englisch? - Excuse me, do you speak English? lit: Excuse me, speak you English? While you can usually count on people in places such as the airport, touristy shops, museums, etc. to speak English, I've found it is good to be polite.

Wo ist die toilette / wc? - Where is the toilet / wc? Note the -e on the end of toilette, and remember that wc is "vee-see."

Aside, a good thing to study up on before you go is German food words. Reading a menu is very important as not all restaurants will have an English menu, and some may not be translated well. ESPECIALLY if you have any food allergies or dietary needs. Zucker, sugar; Fleisch, meat (always with prefixes such as Rind, which is beef, but not hamburger); Champignon, mushrooms (I have only ever seen Pilz used on a menu once); Zwiebel, onion; et cetera. Hausmachte is another word to look for, literally House/Home-made, usually in reference to sauces or noodles or other things that might be bought pre-made. One of my favorite German foods is Käsespätzle, a type of egg noodle mixed with cheese (Käse), and comes from the south-west of Germany.

If you do plan on going to Germany, the biggest thing I can recommend is to learn some of the cultural differences between different regions of Germany. Many Americans have this idea that all of Germany is Bavaria. Lederhosen and Dirndl outfits are not German. They are Bavarian. The giant 1L mugs (Maß) of beer? Bavarian. The big beer halls with accordion music? Bavarian. Bayern ist nicht Deutschland. If you asked someone in the north where their Lederhosen is, it would kind of be the equivalent of a German asking someone from New England where their cowboy hat is.