Best Bait for squirrels, rats and crows!

Rats: 1 part nutella 1 part cooking oil. (They crave the same stuff we do.. Fat, sugar and salt)
Place near normal areas but in clear site of your stake out.
Permission properties with mostly organic farmers (Diary, Beef, Chicken, Goats/sheep, produce/orchards). Rats are pretty obvious where they nest and the farmers can help point out trouble spots.

Mike

Ok this is going to sound jacked up but for squirrels I leave out peanuts in the shell. I have found squirrels do not like to take trash into their holes so they will shuck the peanut before entering their den. They usually sit on their butt to do it. This gives me an unfair advantage and then the peanuts can be reused. 

Crows like corn. Although crows are so damn smart if you shoot a few in one geographical area they won't come back. 

Rats are finicky. Rats I n my area like Nutella but my friends rats won't touch it. My buddy has more success with dunkin donuts tied to a string. So I would say with rats you need to try different bait until you find what they like. 

My wife placed our birds in the cage, on the patio for a few days while some work was done in the house, she also placed a new 5lb bag of mixed bird feed on the ground next to it, all the animals raiding that bag looked like a scene out of Bambi, my watching them from 10' through a screen door didn't bother them much, took 2 days for them to go through it. 

Freshly popped pop corn will drive them crazy. The smell carries well and draws them in. Buy it unpopped and just pop what you need in the microwave. Try not to eat it all first
Red.

Peanut butter only, they liked a lot !

RATS:
At the grain elevator in my younger days we of course had a rat problem. I had a Daisy Model 25 pump BB gun. But was stopped from using it because of the many ricochets. So had to be creative. I discovered that rats love soda as in carbonated cola. After a little experimentation the solution was to place several jar lids filled with fresh cola (Carbonated Beverage) in the evening in the middle of floor away from their holes.
Lights out and here they come. Early the next morning the rats that got to the cola were bloated as footballs...furry footballs...apparently they could not burp up the carbonation. Since I was the youngest at the time it was my job to collect them and dispose of them. They were still alive and kicking but could not reach the ground with their feet, grab the tails and carte them out. I will not describe the carnage that followed as being very graphic. The cats made short work of them and those that did deflate did not make it out of the garbage dump. Could go further as mice were also prone to going for the cola with same results of bloating up to the size of Golf Balls. Many fell victims to an 8 Iron pilfered from Grand Dad's Golf Set . One must understand that was a different time...and kids were kids...I charged a nickel for a bucket of ten to my friends...

Rocky is dead on about the crows. You might be able to buy a caller with a wounded crow call. Just be sure its legal in your area. I have noticed that just about anything likes dry cat food. Cats, dogs, crows, sparrows, starlings and rats also. Only issue with rats is they tend to be nocturnal.

Im a pest control guy. For baiting rats I have found Nutella to be very good, sunflower seed butter is much more attractive than peanut butter, and for those very tough to get rats Silvas Hot Linguisa. The trick is to never use very much, just a smidge in a trap, a little more than a smidge on a plate or open surface. If you can, tie it down or secure it in such fashion as they have to work at it for a bit. Having said that, the absolute best bait is what they are already eating, if its nuts, use nuts, if its fish use fish etc. So before any "control" measures are taken its vital to do some reconnaissance to find out as much as you can about their food, avenues, exits and hiding places. Having done all that, you have the upper hand and will likely not fail. I don't want to come off as a know it all, but with 35 years in the biz, if I don't share what I know with anyone interested it doesn't amount to much. Good luck.