I traveled back in time and accidentally killed my own grandfather! What should I do?MORE ...
First: calm down. Current time travel theory suggests that you've just created an alternate future -- you're not going to disappear, create a universe-destroying paradox, or anything like that, so you have some time to plot out your strategy.
If you return to your present, you will officially no longer exist. This is convenient for a superhero, spy, or otherwise-incognito type. Unfortunately, it's hard to get a job if you don't officially exist, and without one how are you going to pay for all your gadgets?
You might decide just to live through your past and into the future, meaning that -- unlike most time travelers! -- you will have no idea what's to come, since you cannot predict how you've affected the future. This is not a bad way to go; instead of being the creepy clairvoyant who keeps predicting disasters, you will be a fully-engaged member of human society, with the neat bar trick of being able to quickly pick up new technology. See if you can find a representative of a temporalocal time traveler's organization to provide you with fake identification documents, depending on the time period (this will be less important if your grandfather lived in ancient Rome).