ThickIt, mashed potatoes, cornstarch, smooth puddings, bananas, nut butters, etc. can all be used to thicken soups, drinks and smoothies. Of course, everything should be blended smooth.
Crumbly, dry food, along with thin liquids, kernels like corn, skins like peas, crunchy food like lettuce, grains like rice, are all usually best to avoid past a certain point.