Siwa is a conservative town compared to most cities in Egypt. You can photograph the sights and most things but not the women and the female children. I know the restriction on women but not the children so when a group of female children probably 9m - 12 years olds going to school passed by infront of a photo subject, they all said "NO" in chorus.
And then when I was wandering around the foot of the fortress in a local neighborhood I didn't noticed the two women behind the wall and when I started photographing the old house they suddenly appeared and told me not to. So I walked away to avoid any problem.
Photographing men and boys are totally safe, so be careful in taking photos when women are around.
While on the safari by 4WD we found two stray dogs (perhaps abandoned) were running after us. Keeping that in mind some of the girls in group scared off seeing animal feet on the sand (!).
In January, the temperature is not that bad but still a sun-hat and sun glass is necessary. The glass protects your eyes from sand wind occurs occasionally.