And the Someday/Maybe List
If the situation with Bob is more like "Ok Bob, if we meet in the month or two I'll try to remember to give him the book", I'll add it to my someday/maybe list called 'When next ... visiting with Bob'. I do this because I see this as a someday item - I don't really want to see it in my @agendas when I'm in the daily grind. So when I know I might see Bob at a friend's party or whatever, I'll scan my someday/maybe list and say "Ah, maybe I should carry that book with me in case Bob's there".
I do this too with those 'would be nice to have lunch one of these days' conversations. This is the situation where it's not something either of us are really committed to but if free time ever pops up I'd be nice to do it. Those don't go on my action lists because, really, I'm not committed to actioning it right now. Those go on my someday/maybe list under "Visits / Lunches / Dinner to Have". And those I glance at during my weekly review because then I know what my hard and soft landscapes look like in the next week or two and whether I can fit in a lunch or dinner. If I can, then @agendas, @calls or @computer (email) get's a next action to schedule lunch/dinner, and I may even create a tentative calendar entry.