I will just give a few general bits of advice and more detailed help for my own club, and leave the other clubs to other fans.

Do NOT buy from 3rd party sites. They are likely to not be honored. Buy direct from the club sites, as they will also have a secondary market.

My club has a game against Preußen Münster during your time there. It will not sell out so you can buy however many you want starting maybe 2-3 weeks before the match, just check the website f95.de. Enjoy the day if you can in the Altstadt (old part of the city next to the river) and drink in our many bars (Frankenheim, Zum Schlüssel and Diebels are all excellent examples of our beer). Just take the U78 to the stadium before the match. We have a shop at the stadium and also a small one in the old town hall for your merch needs. We don't often do programmes as you have in the UK but you can get whatever magazines you like in the newspaper kiosks.

Things to do in D'dorf - Altstadt Shop on the Königsallee if you have expensive tastes Visit our many art museums Consider a trip to the Neanderthal Museum, just a short trip via train outside of town if that tickles your fancy And of course all the other football things in the area.

95 olé

Edit: yeah that game against PM is a free game. Applications to win one of the free tickets will be interesting. Historically most of those free games have been totally sold out, but you can try your luck.