George the TRex should be used as a boost later in the game. He remains active for awhile, destroying nearby enemies to keep you safe.
Gadgets
Do not worry about purchasing gadgets before starting a new run. However if have the coins, purchase the Ammo Cache to get double ammunition.
Vehicles
If you have a female survivor, purchase The Lady, then save up for the Ambulance. Ignore the Black Bolter, the Road Hog and the Camping Van. Make sure your character matches your vehicle. The Archaeologist, Mechanic, Cop and the Hobo are good choices.
Weapons
The shotguns are the best weapons to use, followed by the bazookas. Make sure to upgrade them regularly while saving to buy the Jackhammer. Handguns, machine guns, rifles, and the Squid Launcher are less effective. The weapons you have available at the start and at checkpoints are random. Make sure you only have effective weapons that are upgraded in your arsenal. By firing your weapons proactively, you can prevent damage to yourself. Repeatedly tap the center of the screen to take out opponents before they have a chance to harm you.