VueMinder Lite USB is a free calendar program that doesn't require installation. It looks good and offers all the features you'd want to stay organized and on time.
You'll have to extract VueMinder Lite USB's executable file from the ZIP file it comes in. When you first open it, you'll be prompted to upgrade to the Pro version, but you can opt out of that. Then just click the tiny calendar icon in your taskbar to view your calendar. The interface is polished and professional, with a standard File menu and toolbar at the top and a large calendar of the current or selected month dominating the lower left of the window. On the right is a smaller calendar, a list of your calendars, and a list of the events for that day. You can add your Google Calendars to the list, which is a nice touch. There's also an option to share calendars, but that requires a paid upgrade. You can customize the look of the calendar, although the default looks fine as is. VueMinder Lite USB offers all the expected calendar amenities, allowing you to add events, set reminders, and schedule recurring events. While the program did freeze up once when trying to access the File menu, it worked well, overall.
If you don't yet have a calendar program and like the idea of one that's portable, this is a solid free option.