I'm a pagan, so it is all about the solstice for my SO and I.
We will typically go somewhere for the sunrise that morning. I have been to Stonehenge and a couple of other stone circles in the past, camping out overnight beforehand - and more recently have watched the live stream from Newgrange. For the last few years we have also celebrated Brumalia - a Roman and Byzantine winter festival that started (in its later period) on Nov 24th. So we progressively decorate the house with lights or holly, ivy, pine cones etc each day from then until the start of Saturnalia on Dec 17th. I have also made an advent-style calendar with chocolates in matchboxes that runs throughout Brumalia - Nov 24th to Dec 25th.
On Dec 5th, which is Krampusnacht and also a Faunalia festival, we will hang a Krampus figure up and have taken to watching the 2015 movie for the last few years.
During Saturnalia itself we will have at least one meal or party with friends - which usually has some element of mis-rule. On the solstice itself, as well as watching the sun rise somewhere or another (probably a local beach this year, as we are on the east coast), there is a local Mummers' play that we usually go along to in the evening. The solstice is also when we do our gift-giving.
On the 26th, there is a Cutty Wren ceremony locally that we will go along to and then there is some morris dancing at another location on new year's day.