When is a Stroller a necessity?

Emily
Started our baby registry last night and got bombarded by staff people giving their opinions about all the best of the best travel systems. While I appreciate their information, my husband and I are struggling a bit when it comes to the stroller bit. We plan to carry the baby on trips to the grocery, outdoor activities etc. When is a stroller most used? Do we really need a travel system that accommodates the infant car seat, or would we be ok with a more inexpensive umbrella stroller? Our budget will be fairly tight and I just don't want to drop hundreds on something we may not truly need.