IMHO the best way forward is wipe clean labels and a chinograph pen (and knife). For the labels, I use the plastic garden labels which look like a T with a square bit on top to write on, and a long thin stalk to stick in the ground. This way, I don't get caught out when I need 7 RVs instead of the 6 I prepared, or something random like Objective GOLD or BLUE 2 Beach or whatever!
Without wishing to get caught up in a model kit discussion (I'm sure there are plenty out there...) I also find that a decent length (couple of metres at least) of a number of different colours of ribbon, plus some chalk, is just about all I need to carry - everything else can usually be found from nature or military kit.
I use the plastic markers from a garden centre as had been said earlier for features. You can always use the reverse of one you don't need and write on it with an OHP pen.
I wrote my callsign (fire team etc) markers on high vis card and sellotaped them around plastic (from ammo tins) so they wouldn't blow away.
I filled two DKP 2 bottles, one green and one blue for linear features. White wool makes good map grids, not forgetting hexy blocks and talc, very useful in low light conditions.
What I did like was the idea of using toy soldiers for the position of the blokes in the large scale model as reccomended by the DS on my JNCO cadre, Cpl D-- P---, D&D (well before they got amalgamated.)
Very chip shop we thought but he emphasised that the guys really would take notice of a model soldier, eg machine gunner and orientate themselves better rather than the pieces of card.
He also put in the scope for humour with some red ribbon for the person who would get shot to emphasise danger areas, very amusing in an O Group.