I have some alien creatures which are essentially land-going octopoids somewhat larger than humans. Tentacles not being a good form of propulsion on land, they have rudimentary 'legs' with one bone each (I envisage something like cuttlebone). Would this be enough for a slow, shuffling walk? Do I need any other modifications to get walking a octopus? This is supposed to be generally cephalopod/mollusk.
Why walk? You’ve got a whole set of strong, flexible appendages. What you need to do is
Consider a snake. It has no limbs, and no issue with locomotion. Your octopoid can use its tentacles in much the same way, flexing a few strong, thick locomotion tentacles and pushing along the floor with them. This helps it stay low and camouflaged in a grassland environment.
Or consider a caterpillar. Their undulating motion would work superbly for your octopoid, who could even take advantage of their omnidirectional tentacles to let them change direction near instantly.
Or consider a worm. Reaching out with the fore tentacles, pushing with the rear ones and dragging oneself along the ground might not be the most elegant form of locomotion, but in the rainy season it could be marvellously efficient.
Finally consider the octopus. Many of the ways octop(uses/i/oids/us) move underwater are still usable on land, especially when they snake their tentacles under each other to create the impression of a rolling, roiling Mass of Tentacular Doom.
Your octopoid will probably also be pretty smart, so switching modes or temporarily hoisting itself into the air atop a column of tentacles to temporarily get better vision probably won’t be too much of a challenge for them.
Having rudimentary "legs" may be enough for a slow shuffle, but another option might be temporarily using the hydraulic pressure of body fluid through the tentacles, much like how a spider walks. A more detailed explanation of how this works can be found here.
Unlike spiders who have joints, your creatures have tentacles (no joints). This may cause serious issues for stability and control, but this changes the specifics how how the motion works, not the underlying concept of using hydraulic pressure.
For example, a sudden "flow" of fluid in the rear four tentacles would cause them to straighten with great force, possibly propelling (as in a "jump") or lunging (as in a strut or "shuffle") forward. The front two tentacles could use the suction for landing and positioning, with the side two for stability (much like how a human might "swing" on crutches when walking).