I’ve got a SBL and seem to remember when I was using it in France was asked what the magazine capacity was a comment was made about it not being legal to hunt with. So bear in mind where you hunt, may have a magazine capacity restrictionDepends on the rifle, and also how much you want to invest in kit for occasional driven boar trips.
Spare magazine is one option, having a rifle sling or belt which holds additional rounds is another. When I went a couple of years back I just loaded one up the spout, three in the mag and then had a pocket full of loose rounds. Once I'd pinged off 2-3 shots I'd pop the mag out and refill it.
Since then I've bought a Marlin 1895 GBL in .45-70 which I would absolutely take next time. It has a side loading tube magazine which holds 6 so you can just feed more in really easily. I would absolutely get a belt which held ammo as well so the ammo was easily to hand.