In the past, I've always stuck to a storyline and minimized the time to travel between two places because I thought the players would find it boring. After riding my motorcycle for 3,500(ish) miles, I gained a new appreciation for travel and just what it can mean in an RPG context.
I think these concepts can be applied to any genre, but what I'm going to discuss will probably apply more to post-apocalyptic/sci-fi and modern settings. I ride a motorcycle that doesn't have a huge gas tank - it's a Honda Fury and it's got a 3.4 gallon tank and is rated at 45 miles per gallon. When I was looking at the specs, that seemed like a great fuel economy. When you do the math, though, you're looking at 153 miles on a tank of gas. Again, it sounded like a good distance, but 153 miles goes fast, especially when the low fuel light kicks in around mile 120, sometimes earlier, depending on the speed I'm traveling.
For overland travel in a setting where resources (especially fuel) is scarce, you want to burn your fuel at the lowest possible rate. Sure, I can get 45 miles per gallon riding at highway speeds (65-75 mph), but I was actually getting about 42-43 at those speeds. Optimally, I wanted to be traveling at speeds from 55-65 mph where I could get 48-50 mpg. So, conserving fuel comes at the cost of taking longer to get somewhere. Sure, your players can opt to travel at top speed, but as the GM, you should introduce the risk of doing that. They might miss something important, such as signs of an ambush, or they might run out of gas.
You Checked the Oil, Right?
Thankfully, this wasn't an issue for me, but mechanical difficulties could be an issue, too. Just like a character's weapons, they need maintenance to function properly. It's assumed the characters are properly maintaining their gear (introducing that would just be unnecessary paperwork), but things can still go wrong. I had a couple "oh shit" moments while I was traveling because I was using some of the improvements I'd made to keep things charged in case of emergency.
The first one came when I stopped and pulled over along the Needles Highway. For those of you who don't know, this is Highway 95 that runs from Interstate 10 to Bullhead City (I took it north from Highway 62, just west of Parker, AZ, to Bullhead City). I had stopped, shut off the bike, and started taking a few photos. I had a USB charger attached to my bike that I connected my phone to so that it would stay charged. When I went to start the bike, it choked. After a few attempts to start failed and the odometer computer reset, I immediately unplugged everything and switched the headlight to low-beam. It started. With a sigh of relief, I had to be more cautious and ran into a couple other instances simply because of the number of times I stopped the bike and shut off the engine along the Pacific Coast Highway. Starting the bike drains power and the bike needs to run for a while to recharge the battery. Or the battery dies. Simple things like this could be introduced as environmental challenges during the party's travel between destinations.
A second instance came up toward the end of my trip when I realized one of the bolts holding my sissy bar (the backrest for the passenger seat) had come out and there were only three bolts holding it in place. Losing one more would have been disastrous. I apparently failed my basic mechanics skill check when I put the seat on and I had to get a replacement on the road. Again, I discovered it before something major happened (like the sissy bar coming loose and the bag flying off the bag while I was traveling down the highway).
So, how would this translate. First, if the characters are servicing the vehicle themselves, you as the GM could make those skill rolls in secret. The characters wouldn't know if they were successful or not. Alternatively, you just don't tell the player making the roll what the target number is and leave it with something innocuous like "yep, looks like you changed the oil." Based on the degree of failure, assign a number range on a die that indicates something going wrong.
Example: A player is giving the vehicle a tune-up before they set out for a city on the other side of the mountains. He makes the appropriate skill roll, but he missed the target number by 4. In Savage Worlds, that would be a single degree of failure. In Pathfinder/D&D, that would be falling about 20% short (assuming a d20 roll). As a GM, you decide that for every day of travel, you will roll a d10. On a 1 or 2, (or an 9 or 10 - whichever you prefer), the vehicle breaks down. Now, the players are stuck in the middle of nowhere and need to figure out a way to get going again. Now, you have a scenario that needs to play out.
Running out of gas could always be a fun option, too. In a post-apocalyptic world where gas is a scarce resource and needs to be scavenged means when that happens, the characters need to hunt down more fuel or walk. In a game like Rifts where most vehicles have a nuclear power source, fuel is less of a potential problem, but speed could still play a factor.
If players insist on the top speed so they can get there sooner, assume they consume fuel 10% to 20% faster. Adding potential insult to injury, the driver/pilot needs to make skill checks to avoid terrain obstacles. Failure means clipping a rocky outcropping and potentially damaging propulsion or drivetrain. It's also possible the driver/pilot could simply lose control, completely wrecking the vehicle and leaving the party stranded. Now what do they do?
So, travel shouldn't be something glossed over in a game, especially in a fantasy setting where traveling distances greater than 10-20 miles is a long journey. If your players decide to travel a great distance or if the campaign requires it for some reason, find a way to make the journey part of the story. Traveling a long distance isn't nearly as simple as heading down the road/trail/galactic space lane and there's plenty of opportunity for roleplaying experiences.