I would like you to tell me if my understanding is right.
1. There are so many things that we can't afford = There are so many things which we can't afford.
"that" in the above sentence is a relative pronoun. (conclusion: we cannot afford (to buy) so many things.
2. There is so little time /that/ we can't have a good time = For lack of time, we can't have a good time.
"that" in the sentence is a conjunction, part of the structure "so" ........ "that".