If he owns a 370z, even a Hotwheels 370z would be cool. (you might want to ascertain whether he already has one.)

If he has a garage, or big apartment, a banner might be cool. NISMO was/is Nissan's racing/motorsport subcompany, so something like this might be interesting:
https://www.amazon.com/s?k=nismo+flag

Does he have a preferred detailing brand or product? (griot's garage, chemical guys, or whatever he preferred?) you could give him a giftcard to that company.

Clothing can be a good idea, but slightly risky. He's a guy, so you could probably get away with asking him if he has a favorite car shirt or one he would want to buy without him realizing your plan to improve your odds of picking something he likes (e.g. not tacky). Personally, I think something like this would look good.

https://www.ebay.com/itm/305833549071?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D275637%2C275255%26meid%3Da1f7b0aae233469396518c3fcc6af1b3%26pid%3D101224%26rk%3D4%26rkt%3D5%26sd%3D144126721717%26itm%3D305833549071%26pmt%3D1%26noa%3D1%26pg%3D2332490%26algv%3DDefaultOrganicWebV9BertRefreshRankerWithCassiniEmbRecall%26brand%3DUnbranded&_trksid=p2332490.c101224.m-1

If you wanted to splurge, I always thought these were cool. (there may be other brands doing the same for less money.)
https://www.blackartgraphics.com/products/370z

Depending upon your BF's taste, he might find a motorsports book interesting.

Just a couple thoughts.