The maps alone... Even if I don't carry all the maps all the time, I'll be able to stay out longer on explores and still have inventory slots for new (and old) maps and all the loot i found on the way...
However, nothing is quicker and more efficient for long-distance exploration than elytra. Not even close.
Nice for exploration/sight-seeing, but for commuting along an established route between distant houses/villages, I'd rather just hop in a minecart. And then save my gunpowder for important things, like fireworks shows and what-was-i-thinking-scale landscaping projects.
To be very clear, let me give another real-world example. On a whim and just for the fun of it, I recently flew about 25,500 blocks (25.5 km) to a woodland mansion, stopping a few times along the way to sight-see, built a waypoint, cleared the mansion, and then returned home all in the span of a couple hours or so of exciting, entertaining gameplay. That includes all logistical time, of which there was none to speak because I'm just flying over there. Compare that to my epic jungle-seeking expedition, the vast majority of which was a wearisome slog. Not to mention the danger. Imagine if I had accidentally rode my horse into a lava pit, off a ravine's edge, or into water with downward current. Now, I'm stuck in a far off land with no horse and not enough food to last for the long walk back. There's just no comparison at all!
Food's easy on the road - i like to use my flame-enchanted bow to top off my stack of whatever i'm eating, but you can always stop somewhere for the night and cook. If you were able to salvage his armor and saddle (or if you've found more on your travels), you can tame a new horse - I don't even know how many temporary mounts i've left "parked" on random beaches all over my world. Not saying that flying above it all isn't quicker/safer, just that there's lots of fun adventure to be had on the ground as well. I ended up staying at my woodland mansion - more about the loot/map transportation issue (which of course shulker boxes would have solved, had I any) than the journey itself; after clearing and securing it, I started long renovation/landscaping project (the mansion was half in a lake, half encased in mountain-with-woodland-forest-on-top ("ground" level where it touched the house was generally between the lower and upper roof; mobs could just stroll out from the forest onto the roof of the house. first thing i did was fix that)), re-building my stores of resources, exploring all this new distant land and establishing new trade routes with new villages. It was kind of like starting over, but without the initial slog just to get a decent set of tools/armor/weaopns. I explored in the general direction of "back home", connecting villages/points of interest to my rail network one station at a time; tunneling at mining levels means i can combine those activities, along with lots of caving and mineshaft-raiding. Once I even hit an ocean monument along the way, which may have delayed completion of that rail segment but was a fun little diversion.
But, that's just long-distance travel, only one aspect of why elytra are so great. Besides that, elytra are just plain fun. It's thrilling to rocket from a ravine's floor into the sky. It's a blast roaring between the banks of canyons and through mountain formations. Diving off my castle's tallest tower and plummeting at break-neck speeds toward the rapidly-approaching ground just to pull up at the last instant is exhilarating.
I can't wait to dogfight the Ender Dragon in an air-to-air duel.
Now, *that* sounds like fun. Don't get me wrong, I'm definitely looking forward to getting my hands on one and flying around; I just don't think it'll become my main method of transportation.
Elytra turned kings into gods.