Cell phones in the past would be hard to do, cause the cell phone towers would not exist yet, it would be hard to setup the networks and carriers back then.
I would take compact devices like the ipad, media players, gaming devices, and I'd introduce touch screen technology and thin displays way back then. If I could bring thin LCD displays and touch screen back to the 50's let's say, maybe by now we would be on our way to having real holographic projections by now and real paper type displays you can roll up and hang.
I would also take the CPU back in time, the latest for PC, Mac, Arm etc... take them all about in time and let the engineers have at em. Maybe by now we'd be closer to Quantum computing or something, or at least really small and really fast CPUs much faster than we have today.
Wireless technology is a good one to bring back to the past as well, anything that could improve upon transmission speed, distance and signal strength now would be great.
Though cars haven't changed much, other than adding in computer components and design, I'd bring a modern car back into the past. Though they wouldn't have the computer systems to replicate the designs, they could look at a modern car for ideas, inspiration, and perhaps we'd see cars evolved in the now because of it.
I would take all the plans and all the designs for space travel that we have, for every type of ship, and go back and give it to NASA and JPL early, cause our space program is really lagging, and this might change things, if real results were seen sooner like a moon base and regular space travel to the moon.
Most importantly though, I'd take the winning lotto numbers into the past, and win.
