I have to drill a couple of holes through my balsa core deck for a new spinlock jammer. I am wondering if epoxy is epoxy is epoxy and therefore I can fill the first oversized hole with this stuff which is only $3?

For $3.00 it's worth doing a test piece that's not on your boat to see if it sets up properly, cross-cut the test piece to see it infiltrates the test piece as epoxy should and will it be fit for purpose.
You are going to need a filler such as Aerosil for that job as well so you may as well buy some bulk epoxy and get used to it.
www.ebay.com.au/itm/Aerosil-1-Lt-Filler-for-Polyester-Epoxy-Resins-FREE-FREIGHT/131772036077
If this is the same epoxy as here;
www.bunnings.com.au/utility-25ml-slow-setting-epoxy-adhesive_p1662637
I have used it for small non-critical jobs but it is not slow setting as it is advertised. Rather around 10-15mins setting to hard glue set time - ok full cure will be more probably 6-12hrs plus depending on temperature but a slow setting epoxy is at least 24hrs setting to hard and full cure 3-7 days. I wouldn't use this for your purpose as expect it won't bond out into the balsa core suitably and make a long term solution. Same as I wouldn't use 5min Araldite for this job - rather 24hr Araldite or a West System product, or a Norglass epoxy glue. Epoxys are not epoxys. Balsa core sandwich panels are great when they are intact but when fittings are not bedded in properly they can become an issue. The web has hundreds of articles - see the 7 parts of this TP52 restoration as an extreme example.
www.sail-world.com/news/234311/J-Bird-III-Restoration-Series-Part-7
I agree a well found small boat should have a litre of good epoxy and a selection of fillers & maybe some glass tape at hand
Use six10 west system epoxy in tube. Self mixing and you can add fairring to it.
Great quality product.
www.westsystem.com.au/west-system-six10/
Use six10 west system epoxy in tube. Self mixing and you can add fairring to it.
Great quality product.
www.westsystem.com.au/west-system-six10/
And only $32 for 190ml. Someone is extracting the urine surely!
Best deal is to buy one of the 5:1 epoxies from one of the major mixers in either 1 kg packs or 5kg packs and a decent set of digital kitchen scales. Stick with the one brand of epoxy and get used to it. I have bought a few 5kg packs from these people lately.
www.ebay.com.au/itm/132952251632?hash=item1ef4925cf0:g:i58AAOSwBOladjlr
If you are only mixing small amounts of epoxy it is critical that the mix ratio be very accurate. With large batches a gram here or there doesn't have much effect on the overall strength but as the mixes get smaller the margin of error increases drastically, sometimes to the point where the ratios can be out by 5 or 10 percent.
Also be very sure to read if the mix ratio is by weight or by volume as that can introduce a huge error if you get it wrong.
There are big arse syringes you can buy at most resin suppliers that allow you to accurately mix the two components.
Ensure that all components are mixed for at least two minutes before applying.
The little syringe that is used to dispense paracetamol to kiddies are good for small measures as they don't have a nib to take the hypodermic, wash with meths pull apart & dry, also they don't have a rubber boot on the plunger, more of a built in oversized ring on the plunger, beware of cleaning them with acetone the writing on the gauge will disappear
I have to drill a couple of holes through my balsa core deck for a new spinlock jammer. I am wondering if epoxy is epoxy is epoxy and therefore I can fill the first oversized hole with this stuff which is only $3?
As long as you are not concerned with strength and temperature is kept below 50C it will work. I've only used the Bunnings stuff to glue some brackets inside the car and they all fell apart after leaving the car in the sun during summer so it likely has a slightly lower softening temperature then the stuff used for boats.
I second the use of syringes for measuring out epoxy and even small amount of 2 part paints.
I found the cheapest place to buy syringes is from a chemist in either 20 or 50mL sizes. The hardnes does strip the marking/labels of the syringe.
I even have a giant 700mL syring I use to suck my bilge dry. I suck it up and spray it out the window.
I find the west systems hardeners 205 and 206 don't remove the scale numbers on the syringe where as the 105 resin will. The hardeners also wash out of the syringe simply with water although I rarely wash them.
I also buy the syringes from the local chemist but I have been using the same two 10cc syringes for years.
I have some resin decanted into small containers for small jobs where half a teaspoon of epoxy is needed. Place the mixing container on to a jewellers digital scale and just drip the resin and hardener direct from the containers. No waste from syringes.