Not sure about Calcium, but foods rich in the Amino acid Tryptophan aid sleep and relaxation. One of the major sources is... MILK. Along with a few other goodies it contains it's one good reason to have a nightime milky drink.
I find sweet tea actually helps me sleep, especially if I wake in the middle of the night.
Leave the radio on low, some think talky like R4 works for me.
In fact my DAB also plays soothing Forest rain or waves on the seashore to aid sleep.
Bedtime reading is good too.
Cracking one off also works.
If in doubt... do all of them; Milk drink + Book + Radio + Quickie...