My brilliant idea of the day is reeds. Yes, reeds. Why reeds, though? Well, for a variety of reasons.
I've always loved that the game featured a variety of terrain types, but many of them serve little purpose. It's fun that swamps received dragonflies, and I've always loved the cattails (and other "fluff" such as ferns) as well as grassy sprays across swamps, but they could use some more love! My idea and suggestion is to add reeds, the order of plant home to swamps, rivers, and general wet places the world over. They would be randomly generated just like the other foragables. Besides looking sexy-awesome, however, what else could they do?
Reeds have traditionally been used for a variety of purposes. As pertains to the game in my mind, reeds could be used in the production of parchment/paper, or, specifically the well-known "paper" made from a certain type of reeds: papyrus. Hides are useful for many things, but are they really worth using for parchment? I do not think hides should be removed from that function, however I believe reed parchment (or papyrus if you'd prefer it to be) could be a cheaper and relatively easier to find alternative (which would decay faster, if relevant). It would give parchment access to newbies, but also just make parchment a more common and useful item in order to leave notes for others, or anything else you can think of. This, in my mind, would be its primary use.
In addition to the above, reeds, if desired, could be used for roofing (as an alternative to pine boughs) as "thatch," a doormat, furniture I suppose, food (the roots) if you really wanted (or in a recipe), some baskets, an ingredient to bricks and adobe (although that's not advised due to bricks not needing plant fiber in H&H), as an alternative to plant fiber (a cheap alternative as it doesn't need to be grown yet you cannot control its quality because it's a foragable, but perhaps it would need to be tweaked as to not make certain items like clothes and the herbalist table too easy to access as a newbie, although then again, as stated, its quality would, in most cases, be quite low), a blowgun as I've seen asked for at least once in the past, a flute/recorder/etc (been plenty of instrument suggestions, I know), or in the use of books (yet another multi-time suggestion item). I suppose you could make an old school Egyptian reed boat, too (or a mini one as a curiosity or decoration).
These are the reasons why I think reeds would be a neat addition to H&H. World flavor and additional items to make are always in demand!
Edit: I should mention that hemp can do nearly all that stuff as well. I think reeds would be cool because of its swamp and riverside habitat, but hemp should also be considered, at least, as an alternative to hide parchment.