KILLSTREAK 1: Care package
KILLSTREAK 2: Sentry Gun
KILLSTREAK 3: Anything (can be Emergency Airdrop)

All you have to do is get your 4 & 5 KILLSTREAK reward or 3 & 4 (with Hardline) and make sure you call them both in at the same time, for some reason the sentry gun influences the Care Package drop.

However, this does NOT always work today I have done this in total about 10 times and 8 times so far have received two sentry guns, the other combination I had was Sentry Gun and UAV Jammer.

Additionally, this can be done with an Emergency Airdrop for some devestating firepower, leading to a possible 4 sentry guns at a time. Both I and AManNamedEric, can confirm this after some testing it equates to 65%. Drop your E-Drop, Sentry Gun and then your Supply Package.