I'd be feeding it fuzzie-hopper mice, depending on the size of them (mice) - as I have gotten hoppers from one supplier that are twice as small as hoppers from another etc etc - Or go pinkie-velvet/fuzzie rats - Also depending on what sizes they are... Most of the stuff I have been getting lately is on the smaller end of the range for what they are called/labelled...:S
Pisces (sp?) brand is SHOCKING for it! I have got "hopper mice" and half were barely even fuzzies, and I have also got ones that have practically disintergrated once defrosted and all the hair fell off and they have popped and guts fell out everywhere... (usually means they are really old or were left ages before being frozen as I have been told... And they always stink and there is poo in the bag and on their fur etc... So I have since steered clear of this supplier/brand and I suggest anyone should also...
And like others have suggested, try not to handle it for atleast a week if you have only just gotten it...as that can cause undue stress and it may go off its food etc - although by the sounds of it, not being fed enough, probably wont, but still...Unneeded stress...
And if you up the size of the food and/or amount you are feeding it, it shouldn't be as snappy, but only time can tell, as it may just be its personality... As I have a pair of a few different snakes, and one will be "tame" as anything and the other will snap at anything that moves no matter how much you feed it... And a couple of my "tame" ones go a bit "green" so-to-speak if you don't feed them enough (amount-wise) or frequently enough...
EDIT: Ok if its a yearling, I'd skip fuzzie anything all together... go 2-3 hopper mice for a while and see how it goes... thats what most of my yearlings are on...(they are all just turned one or coming up to turning one) But it also depends on if it was a late starter too...(as it would be smaller than "normal") but you should be fine on hopper mice

try it and let us know how you go....
P.S. If you are that super eager to handle ur new snake, wait atleast 5days before you feed/handle it...