Why does money fly out when I die

Modern Warfare 3 features the Prestige Shop. Prestige you've performed in a previous Call of Duty games (MW1, World at War, MW2, Black Ops) earns you a single prestige token per game.

Prestige tokens can be spent in the shop to unlock things like an additional custom classes, special emblems and titles, and numerous other features.

Full list (from here):

• Extra custom class (up to 5 extra classes for a total of 10 max)
• Double XP (2 hours in-game time)
• Double weapon XP (2 hours in-game time)
• Regular Package (Callsign Title and Emblem available to those with an extra token lying around)[2]
• Unlock Gear (can be weapons, equipment, perks)(Available at 1st Prestige)
• Hardened Package (Callsign Titles and Emblems)
• Veteran Package (Callsign Titles and Emblems, unlocked after 10th Prestige)
• Reset All Stats (Availble at 10th Prestige)

It is a "secret" killstreak (25, excluding strike package kills, or 24 with Hardline) that's not bound to a specific strike package.

It is similar to the Tactical Nuke in Modern Warfare 2 — using it triggers a countdown, and a bomb drops. However, unlike the Nuke, it "only" kills the entire enemy team (as opposed to all players) and disables their equipment and killstreaks for a bit.

It does not end the match, though it awards double XP for the remainder of the match for the team that used it.