Before us is Mishnah 5 in chapter 6 of Maseches Yoma, which is a direct continuation of the previous Mishnah, in which the ten booths set up along the road from Jerusalem to the cliff were listed.
The words of the Mishnah:
At each and every booth, the people stationed there would say to the appointed man who led the goat: "Harei mazon v'harei mayim" - that is, food and drink are ready and available before you.
Why was he permitted to eat?
Even though they offered him food and water, and even though as a matter of halachah - according to the Rambam, at least - he was permitted to eat, the reason for this is not entirely clear. After all, bringing the goat to Azazel does indeed require sending it to the wilderness, but leading it the entire way as far as the booth is not indispensable, and it is not a condition in the performance of the Yom Kippur service. If so, why should he be permitted to eat? Seemingly, if he could not eat, it would have been appropriate to tell him that he is not obligated to lead the goat the whole way as far as the booth.
"Pas b'salo":
The Gemara clarifies that in practice it never happened that anyone needed to eat. The permission was not meant for actual use, but rather for the matter we call 'pas b'salo', bread in one's basket: when a person knows that the bread is lying in his basket and that he can eat at any moment, he generally does not eat. The psychological effect of this knowledge itself brings it about that in the end he does not need to eat.
Accompanying him from booth to booth:
The Mishnah continues and says that they would accompany him: the people of each booth would accompany the appointed man as far as the next booth - except for the people of the last booth, who would not accompany him as far as the cliff, but would stand at a distance, watching him and seeing him push the goat, without actually accompanying him.
The reason for this: the distance from the last booth to the cliff was two mil, and this distance is outside the boundary within which he is permitted to walk on Yom Kippur. Therefore even the accompanying itself was not permitted, and he would accompany him for one mil only, and from there onward he would stand and watch him from that distance.
Why was an additional booth not made?
The reason they did not set up an additional booth close to the cliff is that the Torah states that the place into which he casts the goat from above is called "eretz gezeirah" - a desolate and cut off place. Had another booth been set up there, the place would no longer have been desolate. For this reason no booth was made in such close proximity to the cliff.
In summary: In this Mishnah we learned about the food and water offered to the appointed man at each booth - a permission that in practice was never needed, and whose essence is the principle of 'pas b'salo'; about the people of the booths accompanying him from booth to booth, and about the people of the last booth who accompanied him for one mil only because of the Shabbos boundary and stood at a distance to see the pushing of the goat; and about the reason that no additional booth was set up close to the cliff, because the place is called "eretz gezeirah" and must be desolate.