Back to the "
Subea Watertight surface marker buoy spearfishing backpack SPF 900":
I notice that it claims to have a 40-Litre carrying a capacity. I think that is
a great size for a "day pack" - although
rather large for a non-bluewater spearing float (7-20L-ish being perhaps more normal). I used a small Black Diamond "Bullet pack", (maybe
16L) for many years as small climbing pack but found it too small other tasks. So I bought a Black Diamond
27L pack, with a clever external pocket for crampons or waterbottle which I've used a lot but, again it was often just a bit too small. So, more recently, I've used a Blue Ice Warthog
36L pack, supposedly "designed by Chamonix mountain guides", it was overpriced and is "stripped down" with very few features but so far that has proved to be big enough for all my day pack needs and with room to spare.
However, I don't normally use a rucksack for carrying my spearing gear, so not sure if that translates to spearing. I often walk in wearing my wetsuit, weight-vest, weightbelt and crocs, so a simple, cheap child's swim bag is enough to carry mask, snorkel, stringer, floatline, waterbottle, torch. For a long walk-in, my single bladder Seatec float fits easily in the swim bag too, although more recently I usually carry my Picasso "plank" float, inflated, on my back, sometimes with a speargun or two strapped onto it. Carrying my, big, heavy fins is probably the most awkward thing -- so the fin pocket and strap are an appealing feature - but it is not bad when my speargun(s) are strapped to the float. What looks to be a waterbottle pocket on the side is a good idea too.
I almost got cooked walking in at the recent Bank Holiday, walking in in my wetsuit. Sometimes it would be nice to be able to walk in wearing shorts and T-shirt instead, with my wetsuit and other bits and pieces in the bag/float (taking care not to forget booties or both gloves!) - - and then maybe put shorts, T-shirt, towel, crocs and car-keys, into the bag/float for the duration of the dive? I suppose I'd still need to wear the weightbelt and possibly weight vest to spare the bag/float but fins and spearguns could presumably be strapped to the float(?).
Nice website with more images, video, etc. on the above product here:
https://www.behance.net/gallery/86739307/SUBEA-BAG-BUOY-SPF900