Most of the ex-hostages were completely secular before being kidnapped, but conducted Jewish practices during their ordeals. Some kept Shabbat; some refused food on religious fast days. Bar Kuperstein simulated putting on tefillin; others prayed. And most have maintained those practices since.
https://unitedwithisrael.org/watch-freed-hostage-segev-kalfon-on-keeping-shabbat-in-gaza/
https://unitedwithisrael.org/watch-gali-and-ziv-berman-don-tefillin/