Stuck for words - By a partner of a prisoner

Dear Prison Widow UK. My partner phones me every night from prison and I visit him fortnightly. He loves getting letters and cards from me but I am stuck for words half of the time because what we've chatted about we've chatted about on the phone.
Obviously we are limited as to what we can send etc so are there any creative ideas via letters that we can engage in together? Have you got any suggestions? Please? Our letters are just repeating what we have talked about on the phone.