For sexy solo time: Girl Scout Cookies
This gets top billing for two reasons: First, masturbation is amazing and legitimately good for you. Second, you can't always have partnered sex due to factors beyond your control -- time, distance, opportunity, etc. -- but you can always make time for self-loving.
Girl Scout Cookies is great for solo sex because it's creative and euphoric, which helps enrich fantasies to make them more vivid. A method I've found super effective is to take a few hits of GSC, pull out my phone, and start reading erotica, and once I'm sufficiently turned on (which doesn't take long with this strain), the phone goes away and my imagination takes over. Every detail in my imagined scenario is so vivid it's almost tangible.
You may not always have time to orgasm, but that doesn't need to be the goal. Instead, you can aim for simply pleasure, which can be enjoyed for as little as seconds at a time.