I like to use a linoleum cutter to cut weeds that are close to a plant (too close to pull without affecting the roots) but long enough to cut and cover with mulch.

I have to agree on the buckets - and the blinds.

Also, coffee filters for lining pots to keep soil from washing out and at the same time keeping slugs from going in.

Coffee cans - for storing kitchen scraps (and used grounds/filters at work) until full - then dumping into the compost heap.

foam peanuts - as filler in the bottom of big pots.

shot glasses - for rooting cuttings in water - fit perfectly on the windowsill!

Corks from wine bottles for orchid mounts. Has to be real cork though.
Buckets are also good for collecting rain water.
The plasic containers cat food comes in, since they have lids, are good to put kitchen scraps in for the compost bin.
Barb

I use the little plastic kiddie chairs from the dollar store to sit in while I'm weeding, planting or transplanting, they are just the right height for me, very light weight to move around - fit in tight places & help avoid back problems from stooping & bending. I sometimes put one over a newly transplanted small plant to shade it from the harsh Texas sun the first couple of days after being transplanted.
I keep them in 3 different areas in the back yard, have two in the garage for the front so don't have far to go when I need one.
Ive used them so many years can't imagine trying to garden without them!

Sour Cream Containers for scooping potting soil

Parmesan Containers (all clear) for fermenting tomato seeds

Starbucks used coffee filters (when I pick up coffee grinds) for lining nursery pots

Starbucks coffee bean bags (sturdy silver) for storing gardening stuff, instant planter for giving away plants.
Am going to use as sandbags when we get into rainy season.

Little plastic apple sauce containers for soaking seeds (morning glory, nasturtium, etc.)

Assorted metal tuna sized and tomato sauce sized cans for rubberbands, pens, etc. If edges are rough, I bend down with pliers and duct tape the inner rim.

Inexpensive plastic silverware sorter for twist ties, plant labels, twine, etc.

I posted a while ago on using CD-Rom spindles for storing twine, wire and the clear plastic tops for storing other stuff.

dreamweaver, if I sat in a plastic kiddie chair, someone would have to pull it off my behind when I was finished gardening! LOL

one of my favorites is a pair of wire cutters that we found in the woods, perfectly good, and I put them to use pruning the miniature roses and an azalea. I wish my big pruners were as sharp.

I second the wire cutter. The best pruning tool ever exists.