Once you have the bags and all the stuff you want to put in there, you need to pack them. This looks like a lot of boring work, but if you have a few people helping you and do it efficiently, it can actually be fun and be done quickly. Put a few tables together and lay out all your material on them. One stack for each item you have. Now you can walk by the tables, take one item from each stack and put everything into one bag. This way many people can work together efficiently without them getting into each others way.
There are many variation of this theme and depending on how many people, how much material and what kind of bags you have, one way or the other might be more efficient: Sometimes it is better to take a bag and fill it step by step, sometimes it is better to first get all material in your arms and drop it in a bag at the end. If you have enough space you might be able to set it up in a way that you can walk in a loop and do some work on your way back. With some bags it is better if you have somebody else opening them and put them at the end of the line ready for the packers to drop their load into them. Experiment a bit and find your best solution.
If you have too many people and they get into each others way, some of them are best employed opening up boxes and shrinkwrapped material and replenishing the stacks of material. They can also get rid of the packing material, rip up cardboard boxes etc. This way the packers don’t need to open boxes etc. in between and can work quicker. They can also take the finished bags and move them where they should go, pack them into boxes or whatever. (Keep some of the boxes your material came in for the finished bags.)
If you do your work this way you will be amazed how quickly it is done. The key is to have enough people. Doing this alone is exceedingly boring, but with many people it has something of a race and is fun (at least for a while).
(Photos are from LinuxTag 2006.)