Haythornethwaite says, and so too does the re-enactor on the hidden page, that many of the Landwehr still carried the large axes they were first armed with even after they were issued muskets. Also I assume that if there was any engineering work happening, such as strengthening a position or clearing an obstacle then most of the actual work was probably done by infantrymen. So a man with an axe would be a nice addition to a Landwehr unit. Variety is good.
Most writers say that Landwehr units made their own unofficial flags. And, I think, they earned them by their performance in battle. So a flag bearer would be welcome.
Extra officers would be useful and might prompt a few more people to support these sets.