Been There, Done That, Got The T-Shirt...

[DeputyJones]

Spellbooks may be a bust since they're mostly useless unless you practice Potter
style magic, which requires specially crafted wands made with materials which
are likely beyond rare in Doug's world. I doubt that Ollivander would be willing
to sell Doug several dozen unmatched wands either.

Just because you can't do something doesn't mean you can't research it or read about in general interest. I can't do martial arts but I still like watching it being done.

Theory books would likely also be a bust since, by the time Doug leaves, he'll
have a better understanding of their spellcasting paradigm than they do.

...Where did that idea come from?

Herbology and potions texts and some seeds could be an interesting but
problematic gift, since Doug could conceivably get in trouble for importing
potentially invasive species from another universe. Besides which, would Doug
really want to risk keeping a stock of magically active plant seeds near his
chaos field for an unknown number of decades/centuries?

I never said anything about seeds, or anything living. Admitedly, if he brings back any well-preserved samples of magical flora or fauna, the science and/or magic of Warriors' World sounds like they may be able to recreate them, but I was thinking more alongs the lines of "Little Wizard's First Potions Set" or something like that as a semi-joke gift.