Now that convertible, zip-off trousers are in common usage, it seems to me that there is extra functionality that they could be providing.
Today’s invention is to replace the circumferential zip usually contained in the leg of these trousers, with a helical one.

One half of the helix would spiral its way waistward from the knee position. The other half, attached to the lower leg, would then be capable of being rotated about the central axis of the leg and then attached by the zip fastener action at any longitudinal position required.
Voila, the length of one’s travel trousers can be set exactly to your individual preference, to work with walking boots, bare feet or as ‘shorts’ of any length you like (This probably requires unobtrusive, or multiple, side seams on the lower leg section to avoid looking as if one has legs attached at the ‘ten to three’ position) .