A bit of flour goes a long way in lieu of cornstarch. I was out of cornstarch a few weeks ago and subbed whole wheat flour (just a half tablespoon) in an apple cranberry pie. It was delicious and really added some depth to the flavor of the dish.

you could use some apple butter in place of some of the sweetener and spices. It is already on the thick side.

Any sort of thickener will do in a pinch. AP Flour, corn starch, potato starch, Arrow root, tapioca powder. Just make sure you know the proportions because too much of any thickener can lead to a gummy mess or worse, a blander flavor.

I like to use either arrowroot powder or tapioca powder. Both work great as thickeners. I like to use tapioca powder is pies the best- I think it makes a silky filling without any of the lumps of cornstarch.

Tapioca is another alternative. The quantities are usually printed on the box.

I usually toss the apples with all-purpose flour, spices and sugar before baking it in the pastry shell and the flour has always been sufficient to thicken the juices that are extracted from the fruit during baking.