I've almost never had pet pal in my parties and I have always ended the game on the high end of the experience ranges people have posted here.
It gives a couple of instances of more XP, but not a whole lot. Often times you can get XP for the pet quests without pet pal.
For example, you can get XP from throwing the red ball to the guard dogs without pet pal, and you can get 1000XP from the dog locked in a cage without having the talent either.
There's also the issue where if you get thrown in jail (how do you get thrown in jail instead of just killed? I couldn't figure that out.), the only way to get yourself out is to have Pet Pal so a rat will bring you a lockpick. No Pet Pal, no Lockpick.
You can get out with displacement abilities, like Tactical Retreat, or an ally can teleport a player out.
I've got a list of early-game things I do to get XP. None of these require combat.
1. Resolve situation with Elodi, Kana, and Burro. 300 for nonviolent, 480 for 2 kills. Can get both.
2. Have a human resolve the situation with Fara. 120 xp
3. Give a Yarrow Flower to Migo for healing ring. 0xp
4. Heal Dain. 240xp
5. Turn in Amiyo's Ring to Magister Yarrow. 600xp
6. Discover the Underground Fire Slug tunnel. Manually dig the spot if necessary (Shovel on the hotbar). 240 xp
7. In the Caverns, Discover the Ancient Stone Hatch leading to Lord Withermore. 720 xp
8. Sneak past the Frogs upstairs and stand next to the water. Standing in this location grants 600XP, for no reason. The frogs won't spawn if the character is sneaking.
9. Explore the hidden path on the beach. The location Gawin would lead the player to. 100xp for discovering the camp and 100xp for some dialog options with Coral, e.g. Jester.
10. Retrieve Griff's Drugs from Stingtail and free Amyro. 240xp when getting the oranges, 840 xp for turning them in, and 840 xp for freeing Amyro.
At this point, you should be some amount of XP into level 2 without having fought anything. At this point I'd recommend a little combat, if not sooner.
Fights in order of approximate difficulty:
Choosing to fight when resolving Elodi, Kana, and Burro.
Kill the lone Fire Slug in the Cavern. 600xp
Corrupted Turtles on the hidden beach. 300xp
Defeat the assassin sent to kill Stingtail. 1000xp for kill, 600xp for saving him.
Kill the 3 frogs.
Kill the 3 crocs. 360xp for kills, 600xp from Gawin. (This unlocks teleport, which gives several new ways to get XP)
