The Tipen: ‘The most striking quality of the Tipen is its size. At 50mm long and weighing only 4.3 grams, the pen stays true to its name. Combined with its lanyard-compatible keyring attachment point, the Tipen offers so many ways to carry it so you’ll never be without a pen. The most obvious way to go is on your keys, but you can also wear it on a necklace, use it as a zipper pull for a jacket or bag, or even carry it loose in your coin pocket or travel wallet’. 5 grams in Titanium. 4 grams in Aluminium: from UK12 (June 2019). This pen is refillable and well-nigh indestructible: both water and fireproof!
I always carry one of these @ 1 gram: https://www.theultralighthiker.com/2016/06/14/ultralight-pen/
And a few leaves from one of these to write on: