Phone people out of the blue, have a gathering.

Honestly some of the best times I remember from late school/uni were just getting random phone calls to go to a friends house or have them come over and we'd just get some crappy Tesco value pizzas, cola and a bottle of vodka or two and just stay up till late playing games together - usually Mario Party or Mario Kart... or even drunken monopoly... just bantering about random stuff the entire time.

Or we'd just go out walking. Like, literally, wondering aimlessly - just enjoying each others company and the weather.