Is it normal that the girl i babysit gets attached to plastic bottles and straws?

Yes. I raised my two siblings, and they BOTH did something similar.

My sister's point of fascination was a rock that she keeps. She drew a lopsided face with a marker and kept it in her pocket. Whenever she didn't know where it was she would s c r e a m. She also talked to it like a diary sometimes.

My brother liked a sock with a dinosaur on it. I ended up sewing stuffing in and adding eyes so he treated it just like a teddy bear. Funnily enough, he STILL keeps it on his bed even though he's about to be 12.

This is especially typical of poor children. We never had money for toys so they made toys for themselves. Affluent kids can do it too though. Sometimes your imagination drives you away from the typical. Kids are just weird bundles of joy.

It takes years for kids to learn all the rules we've absorbed about what's appropriate and what isn't, and it can be very difficult for adults to understand what's going on in the head of small child.

I imagine that in this case, there's something about the size, shape, and texture of the creamer jar that appeals to the little girl. She doesn't understand that her cuddling it seems odd to adults, she just knows it gives her some sort of positive feeling to hold it.

Many children get very attached to a plush toy or some other object. One of my younger brothers had a blanket that he carried everywhere, and for years he slept with one corner of the satin edging stuffed up a nostril. (It may or may not be completely coincidental that he's the only one of my seven siblings who had this sort of fixation, he's the only one of us who went on to get addicted to alcohol and various drugs as an adult, and he has come close to killing himself a few times due to stuff he's snorted.)

As long as she's not doing anything dangerous or destructive, let the little girl enjoy her bottles and straws. If she's content, that makes life nicer for both of you while you're caring for her.