Minimum storage capacity on USB Flash drive

The platform itself is only 10MB and requires nothing on the main PC (no .NET or Visual C++ runtimes needed), but you're wondering is for apps. As for common apps, the best portable browser, Firefox, weighs in at 286MB. LibreOffice weighs in at about 600MB. But that's one of the largest ones. When you're using the platform, it will show you how big each download is and the app's size once installed, so you can plan ahead.