I said the subtleties were messy!
In some cases the service you get will be obvious. GROUND is going to give you an ATC service which will include departure info (which technically is probably Flight Information - I'd have to get the books out to check) so you don't need to ask for FIS specifically.
The question really only arises once you are in the air. When you call up a ground station you have to tell them what you want (otherwise you just end up with an embarassing silence). If you're inbound you're going to tell them that and ask for joining instructions or zone entry elearance.
But if you're just passing by and don't want anything more than to have someone to call if you have a problem then asking for a FIS is probably the best thing to do.
On the final point about asking for traffic info, you example is again fine - and will work with ATC too - but it might help to mention where you are and where you are going so that the person on the other end can tell you about only that traffic that is in your area.