Dog being sick

Hey all, looking for some advice / thoughts on my dog being sick now over the past couple weeks.

1. He’s a Labrador retriever around 3.5 years old.
2. His food hasn’t changed for at least 1 year (unless they have recently changed the recipe).
3. It’s happening at random times during the day, sometimes once, twice or not at all.
4. He’s up to date on his worming / flea treatments.
5. There’s nothing out of the ordinary from his usual diet, even with it being Christmas, he has dry biscuits, wet food, some veg and random treats (not all at the same time).
6. Yes, he’s part lab so he may have eaten something he shouldn’t, but I’d expect it to have gone by now.

We’ve got a vet appointment booked in for Monday, but wondering if there’s any thoughts or advice!