I got kinda inspired by many answers here, particularly the <PERSON> and <PERSON>'s.
A note I will quickly state that there is a strong question 'how do we define civilisation' here. The process of progress in life of humanity started long before homo sapiens was born, not to mention starting agriculture. It started when homo habilis made his first tool. It started even earlier, when whichever homo it was (cant recall) organized his fellows for a first time with speech. I will try to keep to the spirit of Your question the best I can, but please keep this general thought in mind.
1. In my head, some nomads caught on the idea that if they do some field work on the area in which they are at a given moment, on the next year when they pass on that same area it will have more food for them.
2. More food is good, so they slowly started to get rid of plants they don't need, planting the seeds of the plants they like, building some protection against the elements for them. This lead to some minor improvement for them, so the next thing they needed was to always return to the gardens they set up along the way. This forced them to develop geography and navigation, so astronomy, mathematics and eventually writing system for those. Btw their life was harsh and difficult, so I expect codified laws rose pretty quickly and independently in many tribes.
3. Many tribes = many conflicts. Conflicts over naturally rich in food valleys, best hunting spots, rivers richest in fish. Warfare was, historically, the best motor for human development, and probably so it was here. Weapons is one thing, but organisation is another - discipline and communication are a difference between life and death in war. 121
So the conflicts were another motor that driven the development of mobile civilisations.
4. Conflicts and gardens cultivated along the way brought another point. If i cultivated this garden last year, I want to eat from it now. If someone gets to it before me and plunders it's richers, I'm going to be angry. VERY angry. I'm going to build a fortifications around it and next year I'm going to sent in front of me a quick, mobile force with temporary sun and heat shielding so that i am sure that this force gets to the fortress and the garden FIRST and protects it until my main caravan gets there.
5. One of the great questions with this world which pops into my mind is oceans. It's impossible to travel around the earth only on foot. Maybe continents on Your planet are places in such a way that this is possible - but if there are any choke points, I would use them to block the passage for those I don't like for as long as I can, so that they die in the nightwinter behind me - again I would need a mobile force which can hold as long as its possible and then very quickly rejoin the caravan.
6. The oceans bring another point. The first one to master sailing across them gets an enormous strategical advantage. Building ocean worthy ships quickly is tricky, but may be possible - starting with just traveling along the coast maybe (because, You know, big bad tribe is blocking the land passage out of spite), but in the end creating design of vessel which can be built quickly each year, either in great numbers or great scale (massive raft-island?) and is ocean capable.
7. Far into the future, I see Your species advancing technologically to the point they may even have steam or nuclear powered walking cities - still travelling around the planets after millenia, tough perhaps needlessly at this point. But old habits die hard, we, on earth, still keep traditions which have been rendered obsolete generations ago.
On the other hand Poles? Subpolar regions? I don't think I need to elaborate, with right geography they could provide a very interesting alternative avenue for travelling all year round. 537