Don't open the bag, seriously. That alien is probably going to eat you quickly if you do that. Try to stay calm, don't panic.
How, why and what the alien is in your bag can wait. You gotta get out of the building before it wakes up. If you live in an apartment building, down the fire-escape. If not, then out any open doors or windows, even on the 2nd floor. Try to be as quiet as possible. It has good hearing, even when asleep, and when it wakes from a noise it's 3 times as dangerous as if you opened the bag.
Don't stop and wonder who I am, keep moving. Got a car? Don't drive it. It'll notice, trust me. Walk down to the nearest payphone, dial 643-5964-555. Say that the scarecrow is in the fields without a glimpse. You should spend a night at a hotel. The operation will be done Tomorrow at 9am sharp. Do not, under any circumstances, try to go back to your apartment or house before the time period is up. You don't want to catch us in the middle of our jobs, it tends to... disrupt things.
Now, my friend, is the time to stand up from the computer and begin. Do exactly as I say and do not deviate.
There is more at stake then you would ever want or need to know. Just keep your head down.