The best food souvenirs from Germany?

Oh, now I understand, FritschKitchen. I was thinking their taste was pretty awful but couldn't imagine how a terrorist might use them.

Well, sorry about suggesting Ritter Sport and milka... :-) but you know, mass-market does not necessarily equal bad... Anyways, Ruesselsheim is not the most beautiful place, but it is very close to Frankfurt, so if your husband has the opportunity to go there, there is a beautiful place to shop for chocolate called "Bitter & Zart", for Currywurst he should go to "Best Worscht in Town" (several all over Frankfurt) and although Bethmaennchen season is over, he will definitely find them in the more "touristy" shops, or if all else fails, at the airport.
Good luck!

Why are Kindereier confiscated when coming into the US? They are the last thing I would want to bring because they taste awful . . . but banned at the border?

A few ideas: Elisenlebkuchen from Nürnberg, hartshorn and anise oil, which you can use to bake Springerle, marzipan made with honey and no other additives (available in health food stores), Lebkuchengewürz (a spice blend that is an essential ingredient in Lebkuchen, a bottle of Orleans wine produced in Germany--most likely extremely hard to find, Bethmännchen (marzipan cookies, but they may be out of season now that Christmas is passed), and Apfelwein--apple wine--a favorite in that region. I believe aged cheeses (not raw milk or fresh cheeses) may be brought into the US. You might also bring a loaf of Bauernbrot, the sour dough rye.

Mustard!

And I second the curry ketchup, have him eat a proper curry wurst when he is there. I used to live in Stuttgart and I miss curry wursts the most (doners, second).

Also, if they do find Kinder Eggs, they will confiscate them, but I doubt he would be detained (unless he is trying to bring back a case worth). For good chocolate, I second Ritter Sport (although you can find those here) and also After Eight, which is dark chocolate and peppermint, like a York, but infinitely better. A box would be in any grocery store.

These are great, thanks all!! Regarding the location question, he'll be in Rüsselsheim am Main.

I can buy Milka and Ritter Sport at my grocery store. You are better off getting artisanal chocolate that isn't exported to the US.

Much of Europe still has independently owned patisseries, cafes and chocolate shops. Take advantage of that and skip buying a bunch of mass-market stuff you can get here (like the European equivalent to a Hershey's chocolate bar).

It also depends a bit where your husband will be going. You will find the best marzipan around Luebeck in the north, for wine you are better off along the Rhine and its tributaries, from Bavaria, how about some local beer?
Is it allowed to bring (dry) sausages or cheese?
And I agree with others, chocolate in general (I was always asked to bring milka and Ritter Sport) or stuff from kinder for children. Sweets from haribo is also a good idea.

Been there a couple of times, but far from an expert. But I worked for a German company years back and recall fantastic candy, especially chocolate covered marzipan. (Can't recall name, but it had a red wrapper and was a well known brand.) Also Curry Ketchup. Sounds odd, but very popular served on wursts/fries, and really tasty. When I went there for work (Rhine Valley,) I regretted not bringing home wine.

Also, you might ask Luisa Weiss at Wednesday Chef - she's based in Berlin and I'm sure would have lots of great suggestions.

Nothing to do with Germany but I have to share this story about my sister and BinL getting searched after their suitcase was scanned.They were flying out of Newark NJ. The guards found the offending item, good NY pepperoni they were taking to their children livening in that pizza wasteland of Colorado. From the X-ray the guards had suspected they were transporting nunchucks.

I love all things currant. What about Säure Johannisbeeren (sour currant) gummies by Kajte? Near the Haribo gummy bears in a green bag.

Not intended to be eaten but edible nonetheless are decorated Lebkuchen (gingerbread cookies) usually in heart shapes. They are traditionally inscribed with words of love and given to one's sweetheart as a token of affection. My niece just received one from her Austrian groom, inscribed with their names and the date of their wedding!
And as for US airport security, I was stopped and my suitcase re-scanned for a package of DRY pasta...which I bought at the duty-free in Rome...hunh? It seems the rules are random. If you are an honest person, walk with confidence and you won't be stopped.

For the alcohol allowance, if you like sweet dessert wines (for drinking and/or cooking), German sweet Riesling is great. I imagine there is a wider choice there and from some smaller vineyards or producers that don't export to the US.

Illegal items would be meat or dairy, although some successfully sneak these past customs if they aren't searched. It's really a roll of the dice. If found, they will confiscate and destroy. They have some interesting stuff, like gänseschmalz (goose lard) that definitely does not comply to US regulations (like pasteurization).

Safe items would be things like cookies and chocolates both of which the Germans excel at. Your Kinder Egg will make it.

Actual alcohol filled chocolate , the one that has 35% alcohol content on the inside (instead of sugared 5% one like US version)