Storage of stock can become a problem as your collection develops - especially if you purchase from eBay or second hand stalls where there is no box. The other problem is that a lot of the rolling stock these days, comes in a substantial box in itself, which takes up room. Then there is the unpacking and repacking in said boxes - very time consuming.
As I am not a collector of model railways, I am not worried about keeping things in their original boxes to maximise the resell value. When (if) I get rid of something, it is usually because there is something better which has come along and I am happy to get what I can for what I am getting rid of (ideally enough to make inroads into the new items bill!).
So what to do with your stock? Well, if you are like me, and have quite a bit, then a stock box or tray system makes sense. I have made mine to fit the drawers which they live in so their dimensions are specific to that. I can get 8 rows of stock in each tray and the lenght allows for 10 Peco 10' wagons (or the Farish/Dapol equivalent) in each. After that, as far as fitting coaching stock or longer wagons it, it becomes a bit of a jigsaw puzzle to get maximum stock in minimum space. I have also colour coded each tray as it has been built - merely to help me keep track of what is where.
The photo shows one of the trays for the BR Blue era - painted grey. (The blue painted stock trays have BR(E) coaches in them.) Pretty self explanatory. The sides are made out of 11mm pine (cause I had some spare offcuts from another project), backing from 4mm bracing ply (again, spare) and dividers from 3mm MDF (not spare but cheap from the local Bunnings and my saw blade is 3.2mm so the slates fitted in the slots I had cut on the sides to aid location). The gap in the tray is for the Dapol Mk3 Buffet when it finally gets here. Middle column is the Blue Ribband Mk1s from Bachmann, the RH column some previous China production Bacfar Mk1s with GUVs and BGs making up the lot at the bottom (with a couple of Dapol SR CCTs, a Blue Spot Fishvan, the NGS Stove R and an NGS Gresley D113 BG).