Today's lesson, class, is on collation. Game designers always need to be concerned about collation, because their games have to have sufficient parts to function. If possible, always get some promise, in writing from your printer or manufacturer about some guaranteed level of on-target collation. Most important is that all the parts or cards are there, even if they are not in the spot they are supposed to be in the package.
I'm going to focus on card game design, particularly CCGs, where collation is a must have and can be a nightmare. CCGs have decks and booster packs. Deck collation is not a major problem for a professional card printer as long as your decks fill up half of a press sheet or some even multiple of the press sheet (or where they fill up less than a full press sheet and the rest is to be discarded). If they can't get that right, you shouldn't be using them. Very few printers, even card and game printers, have experience with CCG booster collation; they are used to doing the same thing over and over again, not mixing things in a precise fashion. Therefore, you should always ask in advance whether people have booster pack collation capabilities, and whether it will be done by hand or via automation. When collation is done by hand, it is more flexible, but more prone to error. See the article of Cutting Down Costs for more information on how you can cut your costs down on collation.
Now, how does one go about producing the rarities used in random CCG boosters? First off, unless you are selling direct (where you can control who looks at what) you must invest in some type of appropriate opaque, tamper-proof packaging, or you can give up on the whole idea of producing randomized boosters. Period. See the article on Game Packaging for more information.
That said, back to the question of card rarities. There are two main ways that I've come up with (others may have more ways):
I will refer to these as Method #1 and Method #2, respectively, for the rest of the article. Method #1 is harder to totally screw up. Method #2, if you blow the card sorting on the sheets, can end up with "god boosters" with all your rares in one booster, and all commons in others. Both can, really, but Method #2 is more prone to it if you botch your planned collation (or your printer does).
Method #2 is great for controlling the contents of a booster. Why do that when the point of boosters is randomization? Well, if you want organized draft or constructed deck play, you can make sure that people get balanced boosters this way, otherwise unless all your cards are of equal power, the boosters will be of random power. In games where some cards are pre-cursors to play others (such as needing a specific alien homeworld card to play an alien ship card), this Method allows you pair up cards that desperately need to go together with other cards.
For both methods, keep in mind that the contents of a given booster does not have to be random to create a good chase environment for sales. A given card's position within a box or boxes has to be random. So, even if each booster has predictable contents from the standpoint of the designer (i.e., if you see the rare, you can tell me, by memory, what all the other cards in the pack should be), if a given rare's position (people are chasing the rares, mostly, in CCGs) is in doubt, then people will have to buy a lot of cards to find what they want. So, if your card printer puts all the cards in their appropriate boosters and then tosses the finished boosters (sealed in their respective booster pack mylar "foil" pouches) like a salad to mix them, then when people open a box, they won't be able to buy one booster and know the position of all the other rares in the box.
Again, if your packaging is not opaque and tamper-proof, then some nastier folks will "peek" at the contents of the boosters to find what they want.
Collation can be really, really expensive for booster packs, as can the packaging. So you should only think about randomized boosters if you have a lot of money to blow (if you want someone else to do it), or if you are willing to do it yourself and you have bought Game Packaging that you can seal up yourself.
As a parting shot, note that really high end game card printers may have access to automated card collating equipment, allowing you to electronically control the contents of boosters. This is really ideally what you want, and it is awesome if you can get it. However, it is not, by any means, guaranteed. I didn't list it in the methods above because, first, I know less than I should about these collating machines, and second, except for very high end card-specific factories, most printers and manufacturers simply are not equipped for automated collation of random or quasi-random booster packs.