A voter may write-in the name of a candidate on the ballot.
In New Hampshire, both "Bernie Sanders" and "Bernard Sanders" are acceptable and will be tallied together.
You need not specify a Vice Presidential candidate in order for votes for Bernie to be counted, but because New Hampshire does not currently know how it will treat VP write-ins should Bernie win the state, it might be a good idea to write someone in. We suggest Tulsi Gabbard, since we are trying for unity across write-in states, but the choice is ultimately yours.
New Hampshire law does not permit allowing your ballot to be seen by others. This would include distributing a photograph or electronic copy via social media. However, it's perfectly ok to make a copy of your ballot for your own personal record.
(N.H. Rev. Stat. Ann.§§ 652:11, 655:40a, 655:40b, 655:42, 655:43, 655:53, 655:54, 659:17, 667:21)
New Hampshire state law does not require write-in presidential candidates to file any special paperwork in advance of the election.BallotPedia: Write-in candidates, New Hampshire