Even though you can find plenty of MSX cartridges still available today, sometimes you just want to test a game or transfer some files from your PC.
To solve that problem, I use the Leonardo Padial’s SD/MMC reader board. This is truly a great product. It is a bit pricey for us in the US but at the end I think it is worth it. It is simple to use and it will allow you to emulate DSK and ROM files in your MSX pretty easily. Padial also has some good RAM expansion boards as well.
The one problem you might find is around large ROM files. The utilities out there (see a list at MSX FAQ) work well with files up to 32Kb. Even though some tools say they support larger files, my experience is that most times these won’t work.
A solution I found for that was this special cartridge called Mega Flash ROM. It basically allows you to copy ROM files to a EPROM memory in the cartridge and it then emulates these cartridges after a reboot. You can even have more than one game copied at once (the cartridge has a menu boot option for file selection). Many of the larger games like Scramble Formation, Ikari Warriors and Xevious worked great using this option.