The Pelorus River is a great packrafting trip, easily accessible from Nelson. I highly recommend it.
You have two main options - can either park your car at Pelorus and then walk up the track that goes next to the river (starts with a dirt road and then goes into DOC marked track). This option means you can walk up as far as you like and put in when you want, then end up back at the car.
Or option 2 - you can start from the Hackett carpark which is up the Aniseed Valley (Richmond). This option means you can do a walk into Roebuck Hut (a simple DOC hut, 1 hut ticket required), stay overnight and then get going on the river in the morning. From Roebuck Hut it is a 2 day packraft to the Pelorus Bridge (can easily be done faster if you’re keen). You can stay overnight at Middy Creek or Captain Creek Hut.
We put on the river right from Roebuck hut. Didn’t start till just before lunch and we paddled down past both Middy Creek and Captain Creek Huts and camped near where the 4WD track runs next to the river. The next morning we continued to the take out at the Pelorus Bridge and hitch-hiked back to Nelson by around 3pm.
Very scenic, all rapids can be portaged. I scouted maybe two rapids getting out of my boat and did most others by standing up in my packraft - can see most things easily 
Ideally you’ll have a bit of water - in low flows the top section gets a bit scratchy. These pics show the river at an average flow - more water would be nice, but too much water and the river changes completely.
Link to an album on the Pelorus trip:
https://www.facebook.com/media/set/?set=a.721006041316668.1073741833.421608217923120&type=3
Pelorus track info by DOC: http://www.doc.govt.nz/parks-and-recreation/tracks-and-walks/marlborough/sounds/pelorus-track/
There are 4 DOC huts that can be used during this trip.
Cheers,
Dulkara