While German domestic debit cards, called EC-Karte or girocard, (and, to a lesser extent, PIN-based Maestro cards) enjoy almost universal acceptance, this is not true for credit cards (VISA, MasterCard, American Express) or foreign debit cards (VISA Debit/Electron etc.), which are not as widely accepted as in other European countries or the United States. Be sure to check first what cards will be accepted and be prepared to pay cash.
Unlike in some other countries, service staff is always paid by the hour. A tip is therefore mainly a matter of politeness and shows your appreciation. If you didn't appreciate the service (e.g. slow, snippy or indifferent service) you may not tip at all and it will be accepted by the staff.
Since the introduction of the Euro, a tip of about 5-10% is customary if you were satisfied with the service. Nonetheless, service charge is already included in an item's unit price so what you see is what you pay.
Tipping in Germany is usually done by mentioning the total while paying. So if eg. a waiter tells you the bill amounts to "€13.50", just state "15" and he will include a tip of €1.50.
In most restaurants in Germany you can choose your own table. You can make reservations (recommended for larger groups and haute cuisine on Saturday nights) and these are marked by reservation cards ("Reserviert"). In expensive restaurants in larger cities you will be expected to make reservations and will be seated by the staff (who will not allow you to choose your table).
There is a lot of useful information to be found about Germany, traveling and food at this wikiTravel site
Germany has a wide range of flavors (e.g. German, Chinese, Japanese, Thai, Polish, Indian, Italian, French, Spanish, Greek, Turkish) and almost all styles of the world are represented.
Following is a list of some (good rated) restaurant locations in Essen and the Convention location area. Be sure to check out their location on the Celebration Europe II Map
Almost across the street of the Messe Essen is a private brewery house that serves german food as well.
Ruettenscheider House Brewery
Girardetstrasse 2, Essen, Germany
Kapuzinergasse 9, Essen, Germany
Porscheplatz 2, Essen, Germany
Gaensemarkt 44, Essen, Germany
Gemarkenstrasse 122, Essen, Germany
Moltkestrasse 10, Essen, Germany
Ruettenscheider Strasse 227, Essen, Germany
Trattoria Trüffel da Diego
Ruettenscheider Strasse 114, Essen, Germany
Lindenallee 10, Essen, Germany
Rubensstraße 6, Essen, Germany
Rellinghauser Strasse 6, Essen, Germany
Bahnhofstrasse 10, Essen, Germany
Feuerbachstrasse 2, Essen, Germany
Frankenstrasse 423, Essen, Germany
Wegenerstrasse 1, Essen, Germany
Ruettenscheider Strasse 202, Essen, Germany
Special thanks to Armin Jäger for helping compile the necessary information for this page.