Tripods - I spoke about tripods early on, back at the beginning of this blog and I still believe they are the best choice for most things, but on a day hike with a loaded pack on your back you probably don't want to carry a tripod too. A good, though expensive, alternative is a monopod. If you buy the right one, it will double as a walking stick. The best ones have three small 'feet' or short legs housed inside the stick so that when you remove the bottom they fold out like the bottom of a music stand, giving you some additional stability. I know I promised a low-cost alternative - this isn't low cost, but it's excellent for hikers and walkers.
A low cost alternative to provide stability is a bean bag - they are inexpensive and easily fit into a backpack. Cheaper still is to make your own - buy a bag of dried white beans. The drawback here is that they are only good for low perspective (on the ground), or if you can find something higher (like a fence or picnic table) to put them on.
Lighting Accessories - in the studio we can use our reflector umbrellas and studio lights, but for heading into the woods try a totable reflector instead.
They come in different sizes, some come in a set of three, and some come with additional reflector covers like this one. This one is about $50, while not really low-cost, they are cheaper than an umbrella and stand, and easier to carry.
Make your own reflectors for a backpack if you want - a piece of white poster or foamcore board cut to fit the shape of your backpack will be unnoticeable in the pack, help to strengthen it a little and provide you with a handy reflector for little wildflowers hiding in a dark corner. Other things that will also work are a large piece of tinfoil folded up and a locker-mirror (buy this at the dollar store - they are not glass mirrors so they won't break, and they cost, well...a dollar). These will work for bringing light into smaller areas - not for large scenes. For less than $10 you can have three different forms of reflector, all with their own uses.
Plant Clamps - plants clamps are designed to keep a plant from blowing about in the breeze - they are 'posable' with a clamp on the end that will not crush the plant stem. They also cost about $30 or more. Make your own with a package of rubber-coated garden ties (not the plastic-coated ones). Rubber coated ties come on a roll, they are thicker than normal ties and soft because of the pliable rubber coating. Simply wind one end around the plant stem and the other around your tripod or any nearby stable object. Buy this at the dollar store too.
Lighting - Lighting? For outdoors? Well, yes you will come across many occasions when fill-flash is necessary, even outdoors. There really isn't a good alternative to a proper flashgun or speedlight. But, there are other things that can be helpful when hiking through the shaded woods. A small-barreled flashlight with a good beam can be positioned to light up just one particular plant, fungus, or even leaf, or can be bounced off your reflector to get just a little more light where you need it. Make sure you carry extra batteries.
Other things I tend to carry in my backpack include ductape (when you've only got two hands, this can be helpful for positioning your 'reflectors', some small c-clamps, and a few 'pushpins' (buy the better quality ones) - these can all be pressed into service to hold reflectors when necessary. I also carry a utility knife (you just never know when this will be handy), a pen and noteback (for recording light patterns at the day/time in areas I might want to come back to and making other notes for future shooting.
Lens Hood - this is important - use it. It usually comes with your lens...there's a reason. I'll leave you to figure that out (hint: glare).
CP (Circular Polarizer) and/or Neutral Density Filters - good ones don't come for less than $30 - and there's not really an alternative for these either. They are worth the cost, so don't skimp. Buy the best you can afford. You know all those lovely pictures you see where the trees are properly exposed and the sky is still really blue or those great shots of trickling water that look like angelhair?...that's why.
So, yes you can buy all the expensive gadgets to go walking with your camera, but if you can't, you can still take great pictures by using inexpensive alternatives.