The battelmat - made of vinyl, often reversible, often neglected by leaving the markings on way longer than they should be, enabler of creative writings, drawings, and simple scribblings, this is a too-often overlooked piece of gear.
If treated well they last forever. I've been using them since the late 80's and I am still occasionally using one of my original mats, though it is a little marked up from the fire it survived 20 years ago.
|One day it's a ruined dwarf fortress full of demons ...|
The big two-sided versions are incredibly versatile - hexes for games like Champions and GURPS, squares for D&D and a bunch of other games, and when necessary you can completely ignore the grid and sketch out an abstract map or a quick picture of something or jot down some notes when needed!
|...then it's a warehouse in Paragon City, waiting to be attacked by Supervillains|
So although it's not really all that flashy any more with the option of virtual tabletops and playing ion top of a screen in some of those over the top gaming tables, the simple battlemat is one of my favorite pieces of gaming gear. One of the kids commented in our last session that I rolled it out on the table like a pirate sharing a treasure map and that's sort of how I feel - it's one of the tactile elements of our hobby, along with rolling dice and shuffling character sheets.
It may be replaced by _something_ down the road, but I've tried Paizo's flip-mats, those interlocking erasable tile things, and dungeon tiles, and none of them is as simple and versatile as the good old battlemat. I do occasionally use those gridded presentation tablets for areas I know we will be traversing repeatedly (so I don't have to redraw) and poster maps have become a thing over the last ten years or so, but those are really only useful for specific situations. Some kind of holographic table thing may be viable someday but that's the only real challenge I can foresee right now for playing around a table with friends. It's simple, relatively inexpensive, versatile, and damn near eternal: the humble battlemat.