We spent several weeks in NICU earlier this year with our premature baby.
I loved the knitted bonding squares (our hospital gave us these) they made me feel closer to the baby and I hoped the baby would feel more comforted with my scent nearby. A matching hat is also a lovely idea; however, depending on how early they are, they may not be allowed to wear any clothes at all at first (if in critical care).
Other things that would have been appreciated are:
A personalised memory box (NICU allow you take everything home as keepsakes but only provided a small box).
A thoughtful card congratulating them on the birth of their child (we didn't get very many of these at first and it felt sad).
A chargeable mini fan. NICU is hot, hot, hot!
Nice water bottle for mum (she needs to remember to drink lots of water in the heat of NICU).
If there is a Costa at the hospital, a gift card would be lovely. Or some delicious snacks.
Voucher for take away.
Magazines/puzzle books - being on NICU is rather boring!! The days feel very long!
Hand cream
But most of all - lots of supportive messages, visits (if accepted) and practical help e.g. dropping other kids to school/ cleaning/ironing etc.