Oh, didn't know that. What's $500. buy in every two hours mean exactly?
Liz
Missouri has a long and convoluted history of its gambling. When the
state first approved gambling, it was for river boats only and they
had to physically cruise the rivers (Missouri and Mississippi).
Gamblers had to purchase tickets for a cruise and couldn't gamble
until the boat was underway. The cruises were for 2 hours, the boat
docked, passengers got off and new passengers got on. If you wanted
to go again you had to purchase another ticket. Early on this was not
possible as gamblers had to make reservations well ahead of time to
buy a ticket. These early versions were only allowed to offer games
of skill (Video Poker and Black Jack) and no games of chance (slot
machines, roulette, etc.). The state set a loss limit of $500 per
cruise (2 hours).
One day someone pointed out to the state they didn't have adequate
rescue equipment to take care of the passengers if one of the boats
ran into trouble while on a cruise. They relented and stopped making
the boats physically cruise on the water and thus gave way to the
'boat in a moat' concept we have today. The last true river boat went
away when Argosy opened their new casino a few months ago.
Even though the "boats" no longer cruised, the buy-a-ticket-and-board
concept lingered on. Then competition set in and first one then
another stopped charging admission -- the casinos still have to pay a
head tax on every "passenger" though. "Passengers" could only "board"
for 45 minutes every 2 hours. When Station (now Ameristar) built
their casino, they got around this absurd requirement by building two
identical "boats" that were mirror images of each other. One
"boarded" on the even hours and the other "boarded" on the odd hours.
Now the longest wait to enter one of their casinos was 15 minutes.
If you ever see this casino a "boat" will be the farthest thing from
your mind, it doesn't resemble a boat by any stretch of the imagination.
The casino lobby is strong and with support of the Missouri Gaming
Commission these silly rules and restrictions have gradually been
lifted. The $500 loss limit per 2 hour 'cruise' is still in effect
but just about everything else is like a normal casino. This loss
limit is controlled through slot cards. Everyone entering a casino
must have a slot card and use it to load a VP or slot machine or buy
in at a table game. A central computer keeps track of the money
gambled and resets to $500 on the even hours. It will not carry over
unused allotments from one session to the next, the only way to do
this is with chips, tokens, or TITO tickets. Machines will not accept
real coins (tokens only) but will accept bills.
This is probably more than you wanted to know but I got carried away.
Sorry.
So first thing on entering a Missouri casino is head for the slot
booth and get a card, you can't get in without one. Your existing
Harrah's card will work so take it along. The cards must have your
signature on the back and you are not allowed to use anyone else's
card (but we do). 
Rick