The obvious and primary mechanism of increasing Cantrip damage is gaining levels, and increasing your casting modifier (for those cantrips to which your casting modifier applies). All Cantrips automatically heighten to the highest spell level you can cast. Thus, for example, Produce Flame, which does 1d4+Casting Mod damage at level 1, will, for a level 7 caster, be a level 4 cantrip, and do 4d4+casting Mod. As you've noted, feats that broadly increase elemental damage, such as Burn It! will work too.
If you're playing with, or are a Bard, don't forget about the effects of Inspire Courage and the boosts to that which are available, which affect your Cantrips as well as the attacks of your martial companions. In fact, it's doubly effective with multi-target cantrips like Electric Arc.
Another option is Metamagic; while there are no direct damage increases, you could, for example, use the Forcible Energy Feat, as a wizard, to impose weakness to a cantrip's damage type in one round, and then use the cantrip again to deal damage of that type in the next round with a bonus. If the target is resistant to the damage dealt by your cantrips, you can bypass some of that with Overwhelming Energy which is functionally a damage boost, though you'll usually be better served by simply casting a different cantrip.
The Eldritch Archer dedication will let you tack your cantrip damage on to a weapon attack, in much the same manner as a spellstriking Magus, dealing the full damage of both. With appropriate weapon runes, this will often roughly double your damage.
Also for an Eldritch Archer, or a Magus, or other weapon damage dealing caster, there is also the option of Spellhearts. A new category of magic item added in Secrets of Magic, Spellhearts function sort of like Talismans; you attach them to your weapon or armor, and they provide a bonus affect associated with those spells. The Flaming Star, Grim Sandglass, and Trinity Geode all provide bonus damage for a round on weapon attacks, following the casting of a cantrip of the linked element.