Fossicking is an interesting activity when you are in the right places, but - apart from gold finding - can't really see a travelling amateur making money from it. The newest types of metal detectors work deep enough for people to be making some worthwhile finds, but you would have to outlay a few thousand dollars on a good detector and spend a lot of time on it. The driver bought a decent detector when we were full time travelling - basically all he ever found was a used bullet and a 20c piece!
We have fossicked at O'Briens Creek (Qld) for topaz and made a really lucky find there of three big chunks of blue topaz. We had driven up to a remote part of the fossick area where a big fire had gone through a few weeks earlier, and they were lying on the surface. Think they must have originally been in thick scrub that was burnt away. Cost us more to get them cut into gem shapes than we ever got back; finished up giving most to the kids.
Spent a month at Gemtree, which was a wonderful place to camp, and found quite a bit of garnets and zircons. The driver had made up a couple of sieves of different sizes and apart from those all we used was our plastic washing dish for zircon sieving water, and a small camp table to save our backs when sorting. Spade/shovel, of course. In the years since then, have sold some of the garnets and zircons, but probably haven't covered cutting costs.
Have spent time on the Qld sapphire fields. The parts of these that are open to the fossicker are so dug over. Our last couple of visits there, we got much better results by buying buckets of gravel wash from claim owners and sieving that. I have some nice bits of sapphire jewellery from such finds, and kids got some sapphire presents, but we never found more than a few stones. Used the same gear as at Gemtree - though when you buy bucket wash they supply what you need to sieve and wash.
Done a little opal hunting too - at historic Opalton near Winton in Qld (great bush camp area); at Yowah area and Duck Creek. Same theme - out of the way spots to camp in a bush setting, but an awful lot of dirt between even specks of anything shiny.

So my advice is that fossicking can be a fun activity when you are in certain areas but - if you are lucky - you might make a few finds that you can have made up into memento jewellery.

Areas that are known for particular gemstones usually have people taking "tours" that take you onto claims, show you what to do and provide equipment. That is the best way to learn.

I too, would recommend you join a lapidary club firstly, you get to go on field trips and learn what to look for and how to go about getting it. You can also learn to cut and polish your own stones - as well as faceting, silversmithing, etc - and have a lot of fun in the meantime.

My best find was a large aquamarine out at Mt Surprise, went on the tour with Mt Surprise Gems to learn the ropes, and got this beauty after lunch, have had it faceted into three stones - absolutely gorgeous. Also got some lovely clear topaz there. Have also been to Yowah and Quilpie for opals, Moralla in Victoria for Moralla crystals, and lots of other places as well - some with a gem club.

It is a lot of hard work for a little money usually, but fun and something interesting to do, and you meet great people and characters!