Eruvin 36: Wherefore Eruv Techumin?

How accessible does the food in the eruv need to be? What if you're a kohen, and you know that some of your food is terumah, and some is terumah that has been rendered impure? What can you eat? What happens if the status of your food is about to change (the next day, for example)? Is it sufficient to be available before Shabbat? What about the case of "tivul yom" (What's What)? It seems that the pre-Shabbat timing is critical for determining the accessibility of the eruv itself. Plus: The new Mishnah, with a rationale for eruvei techumin. Moreover, based on what's happening, the person making the eruv may set one up in different directions outside of the city. And that's true whether your reason to head out of the city is negative (to avoid people) or positive (to seek out those who are outside if the city to begin with). The Gemara establishes apparent contradictions, and then resolves them. Including reasons why you would want to get out of town.