It depends on season and route (just like backpacking.) We tend to bring extras and luxuries I don't bring backpacking, particularly for cooking. The eight is not on your back, so it is a bit more tolerable to me. It does effect bike handling and you do still have to haul it all uphill so it still matters.
Backpacking we do freeze dried or dehydrated food. Unless the route is remote we buy rel food at grocery stores and cook dinner. I usually bring two pans instead of just one for cooking for example. Usually bring some kind of small lantern for in camp.
In general, bicycle panniers are heavier than an equivalent backpack so you will add a little weight there. In addition you will need to carry some spare parts and tools, again depending on the remoteness and the length of the trip.
I have run into all kinds on the road, a number that stick out:
- two different world tourers and one couple. One was two German guys, loaded to the gills, I am sure they were running at about 100lbs including the bike weight. The other was a solo world tourist who had everything (tarp, quilt, extra clothes & food) stuffed into a large bag on his seat. He did not cook, just ate cold food, usually purchased that day at a grocery store. Truly UL or SUL for a cyclist, and this back in 1977 way before any talk of such things was popular.
- A couple that packed fairly light, used walkable cycling shoes, so carried no extra shoes, no stove. Ate at restaurants and then cycled to camp for the night.
- My friend Ken has always toured on a standard road bike, small bag with a change of clothes and a credit card, stays in hotels and eats out.
Lots of interesting options for bike touring!
Long winded answer, but there you have it. To put it in short, take your current base weight, figure roughly 4-12 lbs weight for panniers and a couple of lbs for tools/spare parts and you will have a good idea.