Yeah, daypack is a very loose term. Squeezing the weight into a 25 job might be hard and the pack won't really be designed for it, the back system might be very uncomfortable and the build quality is unlikely to take it.
A 35 to 40 litre patrol pack may well have a frame of some sort, better shoulder straps and a waist belt. A good one may be long enough in the back length to have a hip belt and transfer the load better. It'll likely be built well enough that the seams don't explode half way round.
An alternative would be a climbing pack. My 37litre has carried 20 plus kilos of hardware and rope very comfortably. Aguille alpine are good as are berghaus but tbh there are lots out there.
Personally I'd lob it all in a proper Bergen as they are designed to carry heavy loads with the correct geometry on the back and a decent hip belt. Any extra space can easily be filled with pies and mars bars!