How to make the day of launching your startup memorable ?

Try to do some good charity work along with it. You will be happy and it will be memorable. For example, If you are really, REALLY dedicated towards your startup, On the launch day, plant a tree. It helps nature and would surely make you all feel good :)

Not really about the product launch itself but something I'll do is to keep screenshots overtime of how my product looks like. Easy and light enough to store and will allows me to see my progress. Look at facebook when they lunched, look at it today...