Ok, there’s a lot here, so let me break it down:
GRRM isn’t hugely specific about feudal incidents – we don’t hear about feudal aid (money to pay for the lord’s ransom, to knight his oldest son, or to provide a dowry for his oldest daughter), relief (payment from the heir of a tenant to take up the tenantcy), primer seisen (payment of a year’s profits before relief can be paid by the heir), fines on alienation (a payment when a tenancy changes hands), escheats (reversion of a tenant’s land if they die without heir or are convicted of a felony), wardship (the right to receive the profits of a tenancy while the heir is underage), or the like.
As far as services go, we know from how Robb’s armies form and how Ser Eustace raises his meager forces that there is some obligation to provide military service for a given time.
On the other hand, we have to keep in mind that these aren’t the only sources of income for a lord from their tenants. You also have feudal taxation and whatever share of that a lord got to keep from what they sent on to the king (for example, the Anglo-Saxon Earls usually got to keep “the third penny” from the taxes they assessed on behalf of the king), feudal rents (which were usually set by custom and tradition), and income from their own lands (which also brings up the tricky issue of feudal labor obligations vs. work done by paid laborers).
So there’s a lot of reasons to have tenants beyond military service.