This site address was sent to me in an email. I tried it several times and it guessed right every time. Maybe someone can explain how it works.
regiftable.com/regiftingrobinpopup.html
I’ve got it figured out:
10 -1 -0 = 9
11 -1 -1 = 9
12 -1 -2= 9
…
19- 9 -1 =9
20 -2 -0 =18
21 -1 -2 = 18
22-2 -2 =18
29 -2 -9 = 18
You see where I am going with that.
As a result, 9, 18, 27, 36, 45, 54, 63, 72, and 81 are the only conceivable results regardless of your original number, all of those results correlate (if they were originally chosen) to the same result which is potpurri.
What the site does to make you think it is doing something amazing is it simply randomly changes what the results 9, 18, 27, 36, 45, 54, 63, 72 and 81 reflect, but those results invariably reflect the same item on any given turn.
Yes they are working in progressions of nine, plus I noticed reoccuring placements of certain items. I should have looked at that first…Thanks for checking that out Pav.
Liteninbolt,
No problem. That happened to me on an unrelated number trick a few years ago, you are so impressed with the fact that it works that it takes your attention away from figuring out why it works.
This website actually does a pretty good job with its randomization. Once I figured out that any multiple of nine resulted in the same item, (which, since 90 and 99 are both impossible conclusions to arrive at it would be better if they made those numbers correlate to different items) I tried to find other patterns involving multiples and there were not any. As a result, I came to the conclusion that a base of nine was somehow important, but I couldn’t figure out how until I played the game three or four more times and realized every final answer was a multiple of nine.
In any case, you’re welcome. I’d also like to thank you for posting that, it was a fun game.
One last thing:
If you take any positive real number that is ten or greater and subtract the sum of the individual digits from the original number, the final result will always be a multiple of nine. There is no other mathematical possibility.
Examples:
542
542 -2 -4 -5 = 531
1896 -1 -8 -9 -6= 1872
14,298 -1 -4 -2 -9 -8= 14,274
That is interesting Pav. Numbers can puzzles in and of themselves. 
That’s absolutely right, I have determined another one, by the way. I would say, “Figured out,” instead of “determined,” but I’m sure someone knew about it before me.
If you start with the number three, and do every third number after three (6, 9, 12, 15 etc.)
When you add up the individual digits of each number the result will always be a multiple of three and when you add the result of adding up the digits to the original number, that result will always be a multiple of three. For example:
1083 (Multiple of Three)
1 + 0 + 8 +3 =12 (Multiple of three)
1083 + 12 = 1,095 (Multiple of three)
That rule doesn’t work with numbers that are multiples of two, four, five, six, seven, eight, nothing, only with multiples of three or nine.
Hmmm…interesting, that makes me wonder about other numerical oddities. I think I’ll check the net for others like these.
Now, if you want to see something that’s less gimmicky, go here:
LOL that was less gimmicky? For an hour there, I thought I was on candid internet! 
Not a bad way to pass some time during the wee hours of the morning…