Hi, we're looking forward to our Best of 10 days Scotland tour this week. We've planned four extra days after for our own exploration. We've got our overnight accommodations set and now I am trying to secure the best travel. The train doesn't take us all the way so we'll have to take the bus and walk to our destinations. My question is what options are there for pre-purchasing tickets for both bus and train.
I found ScotRail website for trains super user-friendly to pre-purchase train tickets. Just bring confirmation number and credit card used for online purchase to local train station and use self serve kiosk machines to print tickets or see ticket agent at counter before journey.
Only took bus in Edinburgh, but tourist info office on Royal Mile gave us handy bus route schedule/map - just paid in coins to go to city locations, very easy and reliable.
You don't say exactly where you are going in Scotland after your tour. Have you checked bus schedules? The Inter city buses run by Citylink take advance reservations, but most local buses will require cash payment when you board the bus.
You may still save a bit of money on the trin tickets (not sure about the bus tickets) if you buy npw rather than waiting. Last-minute train tickets in the UK can be exorbitant.
I remember being puzzled about either a price difference or a  schedule [end edit] difference between ScotRail's website and nationalrail.co.uk at some point this summer, so I'd suggest checking both.
If you somehow end up in Scotland without all the bus tickets you need, I believe you'll find the CityLink offices in Edinburgh and Glasgow to be helpful (though buying mid-trip will cost you precious sightseeing time). The fellow at the Edinburgh bus station took the initiative to check on whether a pass would save me money. He determined that it would not, but I appreciated his effort.
Regarding trains it’s not simply buying tickets in advance – it’s the type of ticket that’s important. You must pre-book Advance tickets – they are the cheaper tickets that have limited availability and sell out, but are not sold for every journey e.g. not Glasgow to Edinburgh.
Other ticket types: Off-Peak or Anytime, you can buy weeks before you travel but they are the same fares as you would buy on the day.
Scotrail and National Rail will show the same tickets at the same prices. Any difference in price means you're not looking at the same ticket type.
If you want the best answer to your question best say where you're travelling to.