Eurostar and Gatwick Express
 

If I buy my tickets from eurostar.com, do they issue e-tickets? And is it better in any way to buy Gatwick Express tickets ahead of time, or can I just wait til I get there?
Thanks!

No need to buy GEX tickets ahead of time - you can even buy them on the train itself.

Eurostar tickets are paper tix - if you don't have them mailed to you you will have to retrieve them at Waterloo before boarding.

You can buy Gatwick Express tickets ahead of time, but it's easier and faster to grab them just before you get to the platform. You can also buy them from the conductor on board.

We use Southern Trains from Gatwick to Victoria. The usual fare is £8,90 - but for four adults traveling together, their DaySave pass is £20.

For anyone who might be contemplating a several-hour layover at Gatwick, you might be interested to know that the DaySave pass is good for unlimited travel all over Southern's network in the southeast. So four people going into London for a few hours would pay £2.50 each way for the ride.

The GEX also has a 4-for-2 offer - see the website but unless you are travelling in peak time the Southern trains service is as useful

But if you're arriving at Gatwick and wanting to travel direct to Waterloo for the Eurostar, you have the option of:

Gatwick Express or Southern (cheaper but regular commuter service that may get crowded) to Victoria and bus or taxi from there to Waterloo

First Capital Connect (not Southern) to London Bridge, wait on the same platform for a train to Waterloo East (but I think there are steps up to the walkway into the main Waterloo station).

If you're travelling after November, Eurostar will be running out of King's Cross/St Pancras, and you should get the First Capital Connect from Gatwick through to King's Cross.