Is it safe to plug christmas lights into a power strip or surge protector that's connected to an extension cord?
First off, power strips are not supposed to be plugged into extension cords. Any extension cords you use for Christmas lights must/should be rated for outdoor use. Any outdoor outlets you use have to be GFCI protected outlets. So, get an outdoor power strip with a long cord similar to the one shown below. Plug it into a GFCI protected outlet and stake it into the ground. From there, you can run outdoor rated extension cords to various locations. Most light strings are not three wire but it's OK to plug them into a three prong extension cord. I usually tape the plug to prevent moisture from getting in and tripping the GFCI.