They had food prepared for them.
Rashi says that during the first and last years they had a lot of journeys. But in the middle 38 years, there were only 20 journeys. Even though that doesn't tell us anything about how much time they were resting vs. traveling, Rashi does explain that they were not constantly traveling. There were a lot of resting periods.
What did they do all day? How did they spend their time?
They were learning Torah. As it says in Shemot 34:32
Afterward all the Israelites came near, and he instructed them concerning all that the Lord had imparted to him on Mount Sinai.
Rashi explains based on Eruvin 54b
Moses used to learn the law from the mouth of the Almighty; Aaron entered and Moses taught him his lesson. Now Aaron moved away and took his seat to the left of Moses. Then his (Aaron’s) sons entered and Moses taught them their lesson. They moved away and Eleazar took his seat to the right of Moses, whilst Ithamar sat down at Aaron’s left. The elders then entered and Moses taught them their lesson. The elders moved away and took their seat at the side. Finally the whole people entered and Moses taught them their lesson. Consequently what was taught came into the possession of the whole people once, into the possession of the elders twice, into the possession of Aaron’s sons thrice and into Aaron’s possession four times.
As one realizes when learning in depth, it takes many years to master the Written and Oral Torah.
Seriously, I think that when talking about Dor Hamidbar (D"H) we should assume that their spiritual level was not only understandably different than ours, but different beyond our (at least mine) comprehension.
The Mishna in Sanhedrin 10.3 says D"H don't inherit the World to Come and they are not judged. The simplified approach says they sinned too much, but a more intelligent one holds they were beyond our shallow understanding of the final judgment and the WTC.
In some sense, D"h were practically living in the WTC - world with no physical needs (or all needs met), and spending their [last] days enjoying the closeness to G-d, as it says (Brochos 17a):
העולם הבא אין בו לא אכילה ולא שתיה ולא פריה ורביה ולא משא ומתן ולא קנאה ולא שנאה ולא תחרות אלא צדיקים יושבין ועטרותיהם בראשיהם ונהנים מזיו השכינה שנאמר ויחזו את האלהים ויאכלו וישתו:
The World-to-Come is not like this world. In the World-to-Come there is no eating, no drinking, no procreation, no business negotiations, no jealousy, no hatred, and no competition. Rather, the righteous sit with their crowns upon their heads, enjoying the splendor of the Divine Presence, as it is stated: “And they beheld God, and they ate and drank” (Exodus 24:11), meaning that beholding God’s countenance is tantamount to eating and drinking.
So it appears logical to say they didn't live (as we live), they existed in a timeless reality of "...And they beheld G-d".
That probably addresses the question of how they learned Torah - because they exalted to a higher spiritual level they treated Torah similarly to how angels did (see Moses' argument with angels, Bemidbar Rabah 17).
My biggest problem is how did they manage to co-exist with Dor Ha'Aretz (the generation of their kids) that longed to establish G-d's kingdom "on the Earth below".
I think Torah says it pretty much explicitly (Ex 18.3):
וַיְהִי מִמָּחֳרָת וַיֵּשֶׁב מֹשֶׁה לִשְׁפֹּט אֶת־הָעָם וַיַּעֲמֹד הָעָם עַל־מֹשֶׁה מִן־הַבֹּקֶר עַד־הָעָרֶב׃
... כִּי־יִהְיֶה לָהֶם דָּבָר בָּא אֵלַי וְשָׁפַטְתִּי בֵּין אִישׁ וּבֵין רֵעֵהוּ וְהוֹדַעְתִּי אֶת־חֻקֵּי הָאֱלֹהִים וְאֶת־תּוֹרֹתָיו׃Next day, Moses sat as magistrate among the people, while the people stood about Moses from morning until evening. ... When they have a dispute, it comes before me, and I decide between one person and another, and I make known the laws and teachings of God.”
They were LITIGATING. Think yourself, they had lots of property, livestock, slaves, and they were terribly bored, as you mentioned - no need to hunt, grow crops, cook, wash dishes, not even using the bathroom (חוץ מכבודכם), etc. So they were suing one another just about everything - "this is my slave... this is my piece of Manna... my bull, etc".
They were so "obsessed" with suing each other they needed a total of 78.000 judges (Yitroh's advice Sanh 18) for 600.000 males (let's estimate the whole population to be 6 fold of that - 3.6M), or 2.200 judges per 100.000, while in the USA it's less than 2 judges per 100.000.
I'm probably wildly exaggerating, they had some spare time to argue with Moses, prepare sacrifices, do some politics (Nesiim, Zkenim, etc), sin with gentiles, and, of course, learn Torah with Moses (where available).
:)
