Collect all three gambling magazines. Then, go to Slot Ranch Casino, and
play the large heart-shaped single pink slot machine on the first floor
near the access point to the Food Court. Keep betting the max of $1,000
to win a lot of money quickly. It is possible to win approximately
$1,000,000 every ten minutes. 
Note: Sometimes you may not win anything for three minutes, but then you
may win three times in a row. Just keep playing until you win the desired
amount of money.

Use the Hacker (Flashlight + Computer Case) on ATMs to get $10,000 from
each ATM.

When you see a pile of money ($100) in front of a slot machine, you are
able to win on that slot machine up to five times, and then you will
hardly win on that machine again until you leave the area and come back
again so everything has respawned.