This information applies to most US collectors, who collect full, unopened packs, also called "live" packs. Many European and other collectors seem to collect empty packs. They collect them in various states. An empty pack that has not been altered and still retains its original shape is called a "3D" pack. A 3D pack that has been flattened, like in a book, is called a "flattened" pack. An empty pack that has been unglued and laid flat as it was printed is called a "label." Generally, empty packs in any state are worth about 25% what a full pack is worth. This article addresses the care of live packs since I am not familiar with the care of empty packs.
Cigarette packaging material is considered "ephemera" in the collecting world. It was not meant to last more than 6 months. Having packs as old as 1890, I can tell you they will last a little longer than that, although there is no hope for the tobacco, short of keeping the pack in a humidor - which may ruin the packaging.
It is a good idea to collect soft packs whenever possible. This is the case since it is also highly recommended that one remove the cellophane from the pack the instant it is purchased new. The reason for this is that, most fastidious collectors will want to retain the packaging in its complete state. Cellophane, however, will eventually tighten on the pack and deform the printed packaging - the real reason for collecting. Eventually the cellophane will dry and burst, and then fall off the pack. This leaves you with a crushed pack, and no cellophane anyway. If you remove the cellophane from a soft pack, the pack remains unopened, or sealed because it has a closure strip across the top. A hard pack on the other hand, is technically opened once the cellophane is removed, even if the lid has never been hinged. Hard packs look particularly ugly when crushed by cellophane as well.
Once the pack is out of the cellophane, it is a very good idea never to touch the paper label with your hands. Use cotton gloves if possible. You can get these on the internet. I don't own a pair yet.
Store the packs in polyethylene zip lock bags. PE is good for storing paper since it will not gas off and color or otherwise destroy the paper. The best size for all standard packs up to 120mm is 4" x 6". You can get these from a good archive materials site for about $10.00 per 100, or you can get them from www.Papermart.com
for $18.00 per 1000. Your choice. I am not associated with Papermart in any way, nor have they paid for advertising space. I have purchased bags from them and they are very friendly folks. They also have other size PE bags for your other items and flat 20 packs, etc. When measuring for size, be sure to account for the thickness of the item as well as length and width.
Keep the packs out of the sun, and out of hot or cold temperatures. I don't need to remind you about damp conditions as well. There is nothing sadder than a great pack with water and tobacco stains, and mildew spots.
Please also do not try to repair a pack, especially with tape!!! Egads, this stuff gets ugly fast.
Store your rewrapped packs in a stable container, such as giant tupperware or rubbermaid boxes. I use rubbermaid and have not noticed any chemical smells yet. Be sure to check with your nose once in a while.
Last, don't handle the packs very often. I find that scanning the pack into a database is good for the occassional peak, and then taking them out once a year to check condition and play with them is fine. With 1,500+ live packs, once a year is a lot of work.