Zurich to Lauterbrunnen and Lauterbrunnen to Lake Como - Buy in advance?

Trains are mass transit. Most people here buy tickets mere minutes before travel. When arriving in ZRH I usually buy my ticket (on my phone) while waiting for my luggage to turn up on the belt.

You can however save money buying tickets in advance. The issue however is that discounted tickets are not flexible (normal tickets are good for any train on the route you bought them for) and thus not a good idea when arriving by plane.

However there is one discounted product that can be very useful for you: The Saver Day Pass.
You can buy these here: https://www.sbb.ch/en/buying/pages/kontingent/kontingent.xhtml
This pass is good for all public transit in Switzerland for a whole day.

These you should buy as early as possible as prices do go up closer to the travel date.

In fact I always suggest people to buy the saver day pass for their arrival date as soon as they have their flight booked...

The Saver Day Pass will also cover most of the distance to Como. So consider buying one for the 30th as well. You will only need a ticket for Chiasso - Como, which you can get at the station in Lauterbrunnen before you leave.

What are your plans in Lauterbrunnen? If those plans include the Jungfraujoch then getting the Half Fare Card would be a good idea.

Our plans for Lauterbrunnen include Wengen-Mannlichen, Oeschinensee Lake, and then Schilthorn. We also plan on skydiving while we are there, and SkydiveInterlaken allows extra flight time for 150 CHF that fly's over the Jungfraujoch. We figured we could do that and save some time while still being able to see the Jungfraujoch since we only have 3 nights in Lauterbrunnen. I've been adding up the costs of cable cars and trains and trying to decide if we should purchase the half fare card.