Learn Spanish (Latin America): Necesitamos este termo por si acaso no hay hielo. - We need this thermos just in case there is no ice.

You might be thinking of en caso de que, which always takes the subjunctive. However, por si and por si acaso are special exceptions. When they refer to a possible situation in the present or future, they are followed by the present indicative, which is why we use hay here instead of the subjunctive.

Could I drop acaso and just say por si no hay hielo?

Yes, absolutely! Both por si and por si acaso mean "just in case" and are completely interchangeable here. Adding acaso simply gives a slight bit more emphasis, much like adding "just" to "in case" in English, but the grammar and meaning remain exactly the same.

Why is it este termo and not esto termo?

Este is the masculine singular adjective for "this" when it comes directly before a noun, like termo. You only use esto as a neutral pronoun when referring to an abstract idea or an unknown object (for example, asking "What is this?"). Since termo is a specific masculine noun, you must use este.

Why isn't there a word for "any" before hielo?