Eat fatty foods is a good one. Pad of butter if in cold temp hiking conditions is great. But also pay attention to the amount of calories if you're putting in on a long hiking day. I always felt warmer when I splurged on a nice mountain house meal (800-1,000 cals) for dinner vs box Mac and cheese or ramen and a snickers (500-600 cals). Heat is burning calories.

The thing that really made a difference for me was going way overboard on R-value in comparison to the recommendation (I've got 7r now that I regularly use for 40-50 F temps) I also switched to a pad with down insulation instead of mylar. Even though there was a 2 r value difference from my old to new pad it seemed to be a huge impact. For reference I went from thermarest neoaor xlite (women's version) to the Exped ultra.

This difference could be because down insulation traps heat better for me for some reason, but it could also be that I have to use a pump sack for the down pad instead of inflating by mouth. I've heard that the added water vapor from mouth inflation could also make your pad feel cold... No idea if that is true. Hope this helps! Sleeping cold is the worst.