Matter of logic I guess,
1. Use cardboard roll, tear lengthways to form a flat cardboard rectangle.
2. Fold twice to form 1/4 size rectangle.
3. Tear off small part of one corner so as when unfolded you have a flat rectangle of cardboard with a hole in the centre. keep this torn piece handy.
4. Pass index finger of preferred hand through hole.
5. Execute required bodily function cleaning process.
6. Remove finger through hole, cleaning finger in the process.
7......remember the little torn piece you saved....use it to clean under your fingernail.
Please pass me my coat as I am going out to get new medication and a life

Do I win a seat on the fantasy bus now ???
P. S. Not plagiarised from McGiver's diaries......an old WW2 diggers' anectote