Is it possible to get HIV from sharing a straw or a cup?

No. Simply no. Just as you can't get pregnant that way. Life's hard enough without these kinds of fears. During the bad old days in which there was no treatment, family members simply didn't catch HIV from each other except by sex or sharing IV drug needles. Please relax and enjoy the company of others.
Extremely unlikely. The HIV virus has been found in saliva but in such low concentrations that possible infection from saliva is extremely remote. In theory, however, it would be possible.
HIV is Hard to Get. I will pretend you are smarter than your question implies. Hiv is contracted from direct exposure of blood or semen or other active densely populated body fluids to your mucous membranes. The way one gets HIV has not changed in the 35 years of this epidemic. It is not caught through casual contact of any kind.