Having trouble understanding a phrase from 18.2

From 18.2
I am having trouble understanding the construction of this sentence as it looks like the musst   clause is missing an infinitive at the end. Does it refer backwards to kaufen?

Could it be rephrased to the following in order to show how it works?
Du musst immer und überall etwas zum Essen kaufen
 

Hallo sfpugh, 

vielen Dank für deine Frage. 
Yes, you are right. "Musst" refers back to "kaufen". So yes, you could rephrase the sentence to: Du musst immer und überall etwas zum Essen kaufen. However, the sentence we chose demonstrates how you can stress one element through putting it at the beginning of the sentence. In this case, the infinitive. 

I hope that helps. 
Leah von Rocket Languages

Thank you for the explanation Leah, I didn't realise you could do that.