You can just make your own holdfasts and dogs and dog holes in a bench and with holes bored into it. You can use a pair of saw horses to make the bench and you can make the saw horses just free handing it and sitting on the wood. Any clamping pressure can be applied either with bought clamps or a Greek vice, which is simply some cords or rope wrapped around something, and a stick put in and wound up to provide pressure. Like what is used in a bow saw. You can cut corner protectors so you can clamp a box or frame together too. A set of tightening load straps with a ratchet on them would be a modern take on this.
Paul Sellers has some excellent videos on bench making, but he rarely uses dogs and holdfasts. You can use the dogs and holdfasts exclusively though, including your work and two folding wedges between your work and the dogs and tapping in one of the wedges to provide the clamping force and the sliding "folding" action of the wedge to provide the variable length you need for any work piece that doesn't fit neatly between your dogs, which are of course spaced out to however you have bored your dog holes.
If the legs of your bench are flush with the apron and the apron with the top, you can also bore dog holes and use holdfasts to clamp something like a door to the side of your bench. Maybe make the legs a little thicker to account for the reduction in strength causes by boring holes in them?
Finally you could make yourself a leg vice from some hardwood and any old jack screw or acme screw, say like they use on the bottom of scaffolding. Or you could even cut your own screw in hardwood! That's 'what they did in the old days for wine presses, etc, and eventually that lead to the printing press and the screw cutting lathe, so the sky's the limit man, only limited about how much time you want to put into it.
To cut a screw in a piece of wood without screw cutting equipment: mark the required pitch line on it and chisel out to the screw form you want. You can do this by drawing or printing out a triangle with the required pitch angle on it, or do what Maudsley did and set a knife at the right angle on a sliding carriage set on a straight edge, and press the knife into the wood (or lead or brass or other relatively (to the steel of the knife) material). Then rotate the work, and a spiral of the required pitch will be cut into the work, which can then be finished by hand.
You can make a straight edge by scraping to the rule of threes... so yeah starting with nothing but some iron and some logs, you can definitely cut a screw.