Does anyone knows how to tag that place (such as fuel station) allows rental/refilling of LPG bottles? I see rent:lpg_bottles | Keys | OpenStreetMap Taginfo but it looks like import from chronology
is there any other tagging for this?
At least in Poland many fuel stations and some shops offer this as an extra service, this gas refill is used by people using gas stoves for cooking but which have no gas main connection.
Typical view (photo from Ogłoszenia - Sprzedam, kupię na OLX.pl ):
Take a look at https://wiki.openstreetmap.org/wiki/Tag:shop%3Dfuel
around here there are dedicated shops, e.g. here is an example (“since 1952”), who also rent outdoor gas heating:
https://www.pronto-bombola.it/noleggio-stufe-da-esterno/
While you might be able to go there in person, I think the more typical case is that they deliver to your place.
There is an established tag: https://wiki.openstreetmap.org/wiki/Tag%3Ashop%3Dgas
It also has a picture of a gas station in poland, maybe just use this (amenity=fuel would be technically compatible with shop=gas)?
that seems fitting for standalone ones, less for when say do-it-yourself shop offers it as an extra service
Seems similar to how it works in Norway, as we have almost no gas mains, but many off-grid huts. Petrol stations are often the place to refill/swap them, but the service is just as likely to be at a supermarket.
You’ll need 2 elements:
amenity=fuel
For the main fueling station, and
shop=gas
self_service=yes
operator=[fueling station]
For these DIY refill stations.
that feels wrong
some have similar stand of firewood - and surely we would not tag it shop=fuel fuel=wood ? And the same for stand with fruits / sand / windshield wiper fluid and so on.
I’d need to see an example but at least here in the states it’s very common for fueling stations to have other amenities that I tag as their own node. One I did a few days ago was this Murphy USA station which not only had fuel, but also a convenience store, restrooms, air pump, vacuum, self-service ice, as well as different fuels at different pumps. You can see there was enough items for me to justify a relation not just an extra node. So adding an extra node for shop=gas seems correct to me.
some have similar stand of firewood - and surely we would not tag it
shop=fuel fuel=wood? And the same for stand with fruits / sand / windshield wiper fluid and so on.
I’d definitely not expect to be able to buy sand at a fuel station, fruits also very rare, the general scheme that could be used for such properties is
sells:fruits (unless it is seasonal/rare)
sells:sand=yes
sells:gas=yes
etc.
windshield wipers or fluids are expected to the point that I would not even mention them (also because it’s usually not worthwhile to buy these there)
I guess that ice and snow is of lesser problem in your area (and such sand/salt appears also in say do-it-yourself shops during winter in my area)
That’s good that such tag exists, but unfortunately this does conflict with bigger shops which sell something, but also do gas bottles. The most prominent example in at least German area - OBI. It’s clearly shop=doityourself, but one needs a way to indicate that gas bottles exchange/purchase is possible there.
And even with gas stations it’s the same - they often have shop which sells something more prominent, like groceries or cigarettes, but some also do gas bottles exchange/refill. Putting it all into shop it wrong IMO, I’d expect rather property tag e.g. gas=yes or gas:exchange=yes or gas:lpg:exchange=yes or whatever like that…
I am not familiar with worldwide usage so take that into account with my answer but at least in my local all gas tank exchanges are a separate brand than the operator they are attached to (I.e. Blue Rhino brand propane tank exchange in front of a 7-Eleven fueling station). Additionally, these are exclusively held outside for safety reasons. Those 2 alone would lead me to map the tank exchange as a separate node even if it is related to the overall fueling station, much like the Reddy Ice node from the above relation to the overall station.
A lot of garages sell LPG, where cars can be refilled with gas, along with the usual petrol and diesel, tagged as fuel:lpg=yes.
Most also have exchange for portable gas cylinders, those are usually brand=calor in the UK.
For these I would probably add sells=propane and/or sells: butane to the associated shop object.
One thing that also needs to be sorted with regard to this is what is the product actually called?
Is it gas / bottled gas / LPG / propane / butane … ? 
Using sells for gas instead of fuel:* just because the main object is a shop instead of a gas station doesn’t seem useful to me.
I would suggest the regular fuel tag plus a :bottled suffix.
fuel:lpg:bottled - the usual mixture of propane / butane
fuel:propane:bottled - if the mixture is guaranteed to contain more than 95% propane as required in colder climates.
fuel:gas:bottled - some unspecified kind of gas in bottled
Unfortunately the size of containers matters to the user, so ideally we find a way to add the bottle size as well.
At least we should distinguish between “full-size” bottles like the ones in the picture above and small ones like thos you use for your camping cooker.