Simple, I don't. Most of my purchases are from amazon, and I order and forget. I get reminded once I see it at my doorsteps.

There are few services which you can forward tracking number, and they update you when the status has changed.

UPS shows you how many days till delivery now, and you can have them remind you but it does not work too well, always delayed, but never the else I don't see it being useful as something like tripit at all