What is the best thing to put on a 2 degree sunburn?

Not much. Apply moisturizing lotions to keep it from drying, and this will help some. Aloe is considered helpful by some. If you have actual blistering, then this is a second degree burn, and should be treated with an antibiotic cream-neosporin- until it heals.
Sun burn. Keep sunburn cool with moist cool/cold compresses. Avoid alcohol containing products. Break off pieces of aloe vera plant & apply sap to skin. Consider non-steroidal anti-inflammatory meds to reduce pain. Don’t yank off peeling skin or burst blisters. Seek medical care for severe pain, fever, lack of improvement of symptoms within several days or if a large surface area is blistered.