Icepacks are considered "liquid" once they melt. They are not allowed past security unless they are being used to keep medications cool.
For your snack I would suggest a bag of frozen grapes. Then you will also have a nice, cool, sweet snack once they start to thaw (or even while they are still frozen).
Going by your screen name, I'm thinking you might be flying from Canada?
Don't forget that you go through US customs/immigration pre-clearance in Canada (most of the time). So, you cannot bring fruit and many other foods (possibly including cheese) onto the plane. Of course, many people do (and don't get caught), but you aren't actually allowed.
Anything solid in your freezer? A thaw-and-eat prepackaged product would probably be the best solution. A lot of people will use uncrustables, as the size makes them unobtrusive and they don't make a mess when thawed and smushed.
The easiest option is to bring snacks that don't require refrigeration (or that can go a few hours without it).
We've brought cheese and crackers, without worrying about refrigeration. The texture of the cheese may we slightly different at room temperature, put normal cheese won't immediately spoil.
Thanks. I knew I had gotten in trouble for cheese once (I declared it and they took it), but I think it was because it was unpasteurised brie (and I was coming from Europe - which may make a difference).
The pre-clearance thing can be annoying as you can generally bring whatever food you'd like (barring the whole liquids thing) as long as you eat it before clearing customs/immigration when you arrive. Clearing before you leave means that you face the restrictions before getting on the plane.
If they are under 3 oz. you could freeze a small juice box or gogert. Maybe an applesauce cup? If you buy the little packets of crackers with cheese they don't need to be cold.
Do you have a bag of frozen veggies in your freezer? Peas work fine, and can be eaten as they thaw (call me strange, but my toddlers LOVE to eat frozen peas).
You could also use a ziploc bag of ice, dump the ice before security, and on the other side of security, ask at a vendor to have the bag refilled with ice.
Thanks. I knew I had gotten in trouble for cheese once (I declared it and they took it), but I think it was because it was unpasteurised brie (and I was coming from Europe - which may make a difference).
Totally off topic, but I remember a cooking show where one member of a cooking club brought back unpasteruised cheese from Europe by putting it in a diaper.