Dishes, laundry, water the plants, walk the dog, feed the cat, vacuum, clean the bathroom or kitchen, go pick up milk or something else you need at the store, make you lunch or dinner. My doula told me make a list and when people ask what they can do tell them to pick something off the list. There's nothing they can do to help you with a baby specifically but these things can help you which helps baby.
This doesn't work for all visitors but helped DH feel involved and useful (because he is and this was what *I* needed): diapers, burping, helping me latch for the first week or so until I sort of got the hang of things.
Otherwise things like throwing in/switching/folding a load of laundry (teensy tiny baby clothes make it more fun); meals; errands...
Re: Breastfeeding and help
cook
clean
do laundry
run errands
diaper changes
watch the baby while you nap or do things around the house
bathe and dress the baby at bedtime
Basically anything not feeding related.
DS: 11/8/11 | 9 lb 7 oz, 22 in
DD: 5/22/14 | 9 lb 9 oz, 21.5 in
Otherwise things like throwing in/switching/folding a load of laundry (teensy tiny baby clothes make it more fun); meals; errands...