Question about Lowepro Flipside Trek BP 450AW

Well, it's very difficult to generalise. Depending on what you mean by accessories (Allen key or camera tripod), a jacket (softshell or down coat) and food (1 sandwich or 3 meals).
I am travelling fully loaded with Canon R6 with v-angle, 70-200 2.8, 24-70 2.8, 14-35 4.0, drone Mini3 incl. remote control, box for batteries and filters, case with cleaning stuff and so on is flat and therefore fits in the notebook compartment.
The 7.5 dl thermos flask and the tripod are on the outside. The jacket is strapped open at the back when not worn.
This means that almost the entire top compartment is for food.
So it should fit.

The compartment for the photo equipment is 30 x 25 x 15 cm. I can just about squeeze my Sony lens 200-600 35 cm long into it. Above the camera compartment there is a 25 x 15 x 15 cm compartment for food, rain cover etc. There are also 2 outside pockets for a tripod and drinks bottle.

Yes, there should be room for everything. It just depends on how much food and drink you pack...but the rucksack offers a lot of space.