What I will do is give my players a warning speech about how just because they can dump their spells in a single travel encounter doesn't mean they should do that in a dungeon encounter which is likely to be the first of many.
This is a problem a lot of folks have and there are a number of threads regarding it. The Travel/Exploration pillar of the game doesn't fit well with the 6-8 encounters per day paradigm for many groups. If you are doing a lot of travelling you tend to get only one or two encounters per day and players that conserve resources feel like they are wasting chances to use them. If you then switch to dungeon crawl mode your players may continue to play like they need to use their high level spells quickly and run out.
There was a thread on the boards that suggested changing the random traveling encounter into the random travelling _adventure_. The suggestion was to pre-roll your random encounters then pack several of them into one day. For instance, let's say the PCs are on a 10 day journey with a 25% chance of an encounter twice per day. That should amount to ~5 encounters. Roll them in advance, put them in relative proximity to each other, give them a simple backstory and play it out as its own little adventure as something interesting that happened along the way.
I'm planning on giving that a try in one of my current games.
Here is an example: Using this Out of the Abyss encounter generator
https://repl.it/BFpk
I generated encounters for 10 days and got the following encounters:
Encounter 1:
Rope Bridge
4 drow, 2 giant lizards (merchants with treasure)
Encounter 2
Warning sign (2 shadow demons) - the PCs take a long rest within a mile of the area 2 shadow demons attack them
Encounter 3
Mad creature (duergar) - RP encounter with a mad duergar
Encounter 4
11 Fire beetles
Encounter 5
Ambush: Grell floating near a high ceiling over a muck pit
You could take these 5 encounters, move them around into a different order and turn them into their own little mini-adventure. For instance, maybe they meet the mad duergar and if they play it right they can extract a cryptic warning from him not to stay near the warning sign. But to move on they need to cross the bridge but the drow merchants (slavers?) are there so they will have to negotiate their way past or fight or bypass it. If they bypass it, the have to go through the muck pit and fight the grell and that fight attracts the fire beetles. If they are clever, they could actually attract the shadow demons and lure them into fighting the drow....or something like that.
So instead of 5 encounters strung out over the course of 10 days they get anywhere from two to four in one day. Have one such adventure every 2d4 days or something...
Sometimes a random encounter is just that...a single random encounter meant to give the game world a feeling of being alive with more going on than whatever the interests of the PCs are. But sometimes a random encounter is tied to something more interesting and the PCs shouldn't be able to readily tell the difference. They should always feel a need to conserve resources because there may be more challenges ahead.