Can I use my data from perks before I use my plan data or will it automatically use plan data first?

Depends on the perk and activation time, the nearest data to expire is used first automatically and it's a different metric than the expiration time for perks, which become unusable if not activated.
So if you use a perk with 24 hr Active duration it's likely to be used prior to your monthly data, or gifts which roll over to next month.
But a perk which has the same active duration as a data gift (current billing cycle + next one) should be used prior to your monthly plan data since that is valid for current cycle + next 2 cycles.

@MobileFizzer_VBMV6 said:
Also data gifts are always consumed first, regardless of expiry date.

That confuses me as it is not was I've seen so far. My data is always consumed based on the expiry date. The earliest to expire is consume first.

Is there something I've misunderstood ?

@FizzyH said:
If I activate a perk of data will my plan use that before the regular data?For sure. I always use other datas before those of my plan.

Welcome For sure. I always use other datas before those of my plan. So at the end of the monts I can give unsued dats of my plan becaus we can just give those datas from the plan.

@MobileFizzer_VBMV6 said:
Haven't tried it in a while, of course, it is always possible Fizz change something. But I have seen it earlier in the year that data was consumed from the data gift bucket further down in the list even though the blue arrow was pointing at the top most available data (with the earliest expiry date). Maybe this was never intentional and Fizz fixed a bug? Impossible to tell unless a @Whizz comments.

I've also noticed the blue arrow isn't always showing the current data being used, but it seems to be a display issue and doesn't really effect the allocation.
You can still see the capacity bar near each type of data changing regardless of the arrow.

So your perks always is used before your plan data.

@MobileFizzer_VBMV6 said:

That's not true.

There are screenshots here in the forum that proof that it at least used to be true. For example:
https://forum.fizz.ca/en/discussion/2631056/where-does-data-get-used-from-first
As I said, I can't rule out that it has changed since but, if it did, it is a recent change. I've definitely seen the exact same behaviour as in the screenshot from the thread referenced above earlier this year.

Sure, it could be the case for that user, either due to a fault or the terms of that specific perk.
But it's not true that data gifts are always used first nor that all perks have 30 usage time.
Of course bugs and issues can occur regardless.