Learn Hardcore Japanese: raisyuu no ryokou no koto wo kangaeru to, ima kara wakuwakusimasu. - Thinking about next week’s trip makes me excited already.

来週の旅行 = next week’s trip / the trip next week
Here, の links 来週 to 旅行.
旅行のこと = the matter of the trip / more naturally, the trip as something being thought about
Here, のこと turns 旅行 into the thing/topic about the trip.

So the whole chunk 来週の旅行のこと means the matter of the trip next week, which in natural English is just the trip next week or next week’s trip.

What does 〜のことを考える mean? Why not just 旅行を考える?

〜のことを考える is a very common pattern meaning:

to think about ~
to have ~ on one’s mind

So:

旅行のことを考える = think about the trip

If you say 旅行を考える, it is less natural in this context. It can sound more like:

thinking up a trip
planning a trip
considering the idea of a trip

By contrast, 旅行のことを考える clearly means thinking about the trip in a broad, natural way.