Some things I can think of that would normally get reserved for other members of the team but I think it'd be a fun fun power.
1: Disable pretty much any battery powered object or engine. Frozen batteries don't work. A speeding car can be stopped in it's tracks when a little of the liquid in the fuel line suddenly freezes solid.
2: Convince Steve you have lazer vision.
3: Convince Steve you have supermans freezing breath.
4: Convince Steve you can breath fire.
5: Convince Steve that your animal sidekick can breath fire.
6: Convince Steve that he has developed powers and can breath fire but can't control it.
7: Produce a burst of hard-gamma radiation or xrays by heating a few atoms to obscenely high temperatures.
8: Never need a microwave.
8a: Make Steve think the microwave is broken because no matter how long he microwaves food it never gets hot.
8b: Make Steve think he's going crazy because no matter how long he holds the frying pan over the flame on the hob, it never even gets warm.
9: Create a burst of mist at will by cooling a section of air.
10: Launch yourself into the air by lying on something and flash-heating the air on the other side.
11: Help protect a space capsule from burning up by cooling the heat-shield and dumping the heat into the air.
12: Create a partial vacuum by cooling the air to close to zero so that it turns to liquid or solid.
13: Cut almost any object by heating a very very very thin layer of material.
14: Freeze off any warts or verrucas.
15: Make icecream in moments whenever you want.
16: Perfectly chill any drink.
17: Make it so Steve burns his mouth on poptarts no matter how long he waits before biting into them.
18: Conceal don't feel.
19: Convince people that you're the human torch by cooling the air close to you but heating the air a few inches further out.
20: Play The Floor Is Lava with real lava.
21: Convince people that you have an invisible shield by creating a half sphere of frozen air.
22: Write in the air with letters of fire and freezing air.
23: Convince Steve there's a ghost by cooling the air in the shape of a ghost and having your misty figure float around.
24: Walk on water by freezing it as you go.