I keep a travel journal -- have for years. And I keep notes and sketches from projects around the house in journals.
The travel journal is kept chronologically. The project journals can be dedicated to a single project (like modifications to my 2015 Tacoma) or a collection of many notes and contacts chronologically.
I now make sure to put my name in the front of every one, after losing a travel journal at O'Hare one time (ugh).
As one who's spent his life in the paper industry (starting with a paper science and engineering degree at university), I'm probably a bit fussier than most around paper grades.
My travel journals are
Insiprit Eco Journals. Impossible to find here in the US, so that recommendation is really of no help (mine were brought by me or friends from South Africa). The characteristics I like, which might be a help, are a flexible cover on a hard-bound journal of about 200 pages. A5 size (5-7/8 x 8-1/4 inch / 148 x 210 mm) for my travel journal -- it packs well. I prefer quadrille ruled when I can get it, but I can live with lined pages. The most important characteristic for me is paper quality. I like relatively smooth paper (so many cheap journals have rougher paper for no good reason) with relatively hard sizing (the papers resistance to absorbing water). Hard sizing helps control ink feathering, especially with a rollerball, and can give a bit more dimensional stability. Paper is a very personal choice though, so there's a big component of what-ya-like.
My project notebooks are all kinds of things over the years, but for the last three or four years they've been composition notebooks from Daiso, the Japanese dollar store. These do come in quadrille ruled pages, in A5 and A4 size (8-1/4 x 11-3/4 inch / 210 x 297 mm) with a slight preference for the A4/letter size. I get them when I'm at a Daiso store in San Diego, and although Daiso has an online store, they don't offer the kraft-covered notebooks I get. Nice hard-sized, smooth paper made in Japan -- where they really take care with their papermaking.
Costco sometimes has a 6-journal mulitpack of Moleskine journals. I have no first-hand experience with 'em -- but hey're probably OK -- it's a reputable name -- although the ones I've seen are made in Vietnam, so the papermaking could be anywhere on those from super to crappy. Flexible hard cover, 120 ruled pages in a jjournal measuring 7.5 x 9.75 inch. They come in and out of stock, so like most things at Costco, it's a roll of the dice.
Moleskine is a pretty well distributed brand, though, so it can be found at any art supply store and many other places.
Most of the free notebooks one gets at conferences or trade fairs or whatever go straight into my recycle bin. The paper just isn't very good from my (admittedly snobby) experience.