I carry a very small adjustable spanner for the track nuts. On my earlier bikes, the front nuts and rear nuts were different sizes and needed a 14mm and a 15mm. All the open ended spanners I seemed to find in the shops went up in 2mm jumps, so you could get a 14/16 open ended spanner. Then when on holiday in a French supermarket, found the perfect 14/15mm open ended spanner.
On my current fixed bikes, both front and rear are the same size nuts, but I just carry the small adjustable in my tool bag to get me home.