The problem with playtime before they know you, or their surroundings, is if they get spooked (which can happen easily), they may run away, or escape, and you won't be able to catch them or help them safely. They really need to get used to sights, sounds, smells, of their surroundings before you remove them from the cage. If you NEED to remove them before they are used to all this, you can use a box. Put it up to the cage (most will willingly climb in), and move them to another cage for the time being.
As for snacks, most of us give plain cheerios (it's a BIG hit with ratties), I will once in a while give plain rice crispies one at a time, plain yogurt to lick off your finger, unsweetened applesauce off fingertips, pieces of fruit, I sometimes give raw veggie pasta, cooked rice, baby puffs, I sometimes give a piece of rice baby cracker. There's a list of foods in the reference thread on here.