Iomega Zip Drives can run on optional batteries. Buy a Visioneer PaperPort scanner or one of its imitators if you need to use a scanner in the field. Buy small, battery-powered speakers if you want to travel with speakers. Look for PC cards that can increase the functionality of your computer. Two USB ports have been standard on full-size laptops since the introduction of Windows 98.
Manufacturers continually introduce new types of peripherals.
Something not yet invented may increase the functionality or enjoyment of your computer. Your laptop may lack the capacity to run certain peripherals even if you meet the minimum system requirements. Adding RAM might help. Do not expect a PC card with USB ports to work with a laptop. Inc. How things get done.