Everyone should keep cold or ice packs in the freezer and pull them out at a moment's notice to treat minor sprains and bruises. Immediately applying a cold compress to an injury reduces swelling, bleeding and pain by reducing blood flow to the injury and slowing down the pain signals between nerve endings and the brain.
Apply a cold compress to the area for 20 minutes every 2 hours. Never put ice directly on skin, always wrap it in a damp towel or cloth and then apply.
No ice packs handy? A plastic bag filled with crushed ice or even a bag of frozen peas wrapped in a damp towel will do the trick, and even cold water is better than nothing at all.