My first thought was a straw, but that certainly won't work with chunky or thick soups!
My second thought was to get one of these bibs:
http://www.amazon.com/Baby-Bjorn-Bib-Blue/dp/B00081Q6LI
They are AWESOME! We bought one two years ago. You only need one, because you just pop it in the dishwasher with your dinner dishes, so it's always clean when you need it. (unlike the laundry hamper full of soggy disgusting cloth bibs I used to have!) My son is now 3 1/2 and still wears it.
THE BEST PART is that it catches and holds large quantities of food, especially liquids, without soaking through to the clothes. Seriously, it's so amazing! The only thing you have to be careful about is not to forget that there's liquid in there when you go to take it off. I've accidentally dumped out what the bib so carefully caught for me after dinner. Ooops!
I had a hard time finding them in stores, so i bought mine online. My sister said she found some knock-offs at Children's Orchard, but I never saw them. I don't think we have one of those near us, either. Baby #3 is coming next week. They're no good for newborns, I'm sure, but I think I may have to buy one more just because I can't bear to not have one for my 3 1/2 year old!