Of Time Machines and Birthday Cakes

So, suppose you forgot that monday last week was your birthday. Any reference is purely coincidental. Suppose you felt ashamed that you didn't buy a cake to share with your friends, so that you didn't say it to anyone. You obviously want to amend this.

The first idea that came up to my mind is to devote yourself at creating a new branch of physics, and manage to create a wormhole which acts as a time machine. you then step back in the future, drop to the nearest patisserie/supermarket, buy a cake - you birthday cake must obviously be produced the day of your anniversary. Finally, you step forward in time and you share the cake with your friends. However, since cakes have an 'eat me before ' typically less than one week, you end up witha cake who's rotten. or may be not. but it doesn't really matter, none of your friends is going to believe that it's still good when they see the writing on the wrappings... damn... So much time wasted for nothing...

well, you're left with no friends, but a time machine, and that is reasonably cool. you can always go and look for new friends in different ages...