Rail
Even though in most cases you will find rigidly fixed train tickets, in some countries, such as the US and the UK, there are discounts for those who book late.
Rail passes might reduce your trip's cost, but late booking is also possible with specialized agencies or directly from the rail company. Even so, booking too late bears the risk of not being able to get on the train, but if you're smart, you might be able to grab the price-cuts with calculated risk! This means: the same trip for less cost! What do you say?
Opportunities, Useful Tips, Advice on Last Minute Train Travel
What to Do:
Check the rail company's online system for prices and compare
Find out if the rail company or some agent offers last minute discounts for that particular line or service that you're willing to use. Or, check their online booking system to see the prices of tickets for tomorrow and following days, then compare those prices with ticket prices for later today. You might find difference. But this is quite rare with rail operators, it's not like in the case of hotels.
Usually, the more developped a country is, the higher the possibility to find price-cuts for rail tickets. Also: usually it's the online booking systems that allow late deals. Offline late purchases usually don't come with any discount at all.
Try a specialized train ticket reseller
They might give you discounts. This is mroe likely than directly with the rail company. Because, these agencies buy the right to sell a certain number of tickets, sometimes within packages. You might be in for a discount, especially if it's within a package that they couldn't sell in time.
What Not to Do:
Wait long and blindly risk buying in the last hours
Never risk to see in the last hours, "if there are any discounts", you might not be able to find any more tickets at all.
Hesitate to buy train tickets in advance on highly frequented lines, thinking that late deals might come in
On some routes and with some companies, there are almost no last minute offers for train tickets.
Don't expect price drops on intensely circulated lines, especially during holiday seasons.