Every dive shop will supply weights and tanks. No need for those.
I think that a good arguement can be made for any other item of equipment. I backpack also (or just generally travel with a rucksack and diving gear). I take everything.
Firstly, there is kit you can rent...and kit that you cannot. I don't see many dive operations renting out stuff like DSMB and reel. Every diver should carry one of those. An oral inflate DSMB and finger reel aren't expensive and should be considered. Likewise, a whistle is a good option.
Here's the rest:
1)
BCD.Easy to hire, but all too often these are well-worn and can be beyond safe levels of wear. You can get a relatively inexpensive, but decent lighweight travel BCD, such as the
Zeagle Express Tech, which will cover all your diving needs. Alternatively, look at modular BP&W systems. These are great for travel and are entirely 'future proofed' against your later development in diving. Choose a lightweight aluminium or nylon backplate. Here is a small travel wing"
Oxycheq 18 and a travel backplate to go with it :
Ultra Lite Travel Plate. Badly fitting BCDs contribute a lot to the feeling of 'awkwardness' felt by many novice divers. Getting your own (especially BP&W) will mean you have a tailored solution that will soon start feeling like a second skin.
2)
Regulator. A good regulator is the core of any scuba system. Having your own reg brings peace of mind. Rentals can, again, be unreliable. Stick with a core brand (Apeks, Scubapro or Atomics), but you don't go for the top of the range.
3)
Dive Computer. Some shops rent dive computers, but rental is expensive. Using a dive computer allows much more freedom as a diver (less feeling of reliance on the dive guide), more peace of mind... and will increase your bottom times (due to multi-level profile calculation). I also find that a dive computer
can increase your awareness of depth-time-NDL, providing it is not used thoughtlessly. If you want a small 'watch' style wrist computer, the
Suunto D4 is a good all-rounder. I use a D9... the electronic compass sometimes comes in very handy when out of the water (like when I got hopelessly lost in Hanoi).. or go trekking.
4)
Camera + Housing. People often overlook this... but a housing for your camera can really boost your enjoyment of diving. Underwater photography is a hobby in itself...and you get to take the memories home with you (and make your facebook albums seriously more interesting for your friends). Depending on your existing camera model/brand, the OM underwater housings are usually quite cheap ($2-300).
5)
Fins. A good set of fins can really improve your diving enjoyment. I love ForceFins... less effort, good power...and easy to pack for travelling. If you like your existing fins, then take them
6)
Wetsuit. The easiest item to rent and the least safety implications. If you will be diving in hot climates/warm water, then this isnt a critical item. You could consider an alternative, such as
4th Element "thermocline' clothes... they are as warm as 2-3mm neoprene, but VERY lightweight, quick to dry, machine washable and neautrally buoyant! I use these for all my travelling in the tropics. If your current wetsuit fits you well and keeps you warm, then take it.
7)
Torch. A small diving torch can be useful - for investigating nooks and crannies, signalling or night diving. A 2xAA LED torch for scuba is quite inexpensive. I normally take a small torch when I am travelling anyway... so getting an LED diving torch kills both birds with on stone. Have a look at '
Aquatech' Aqua-Star 1W torches... which offer great value.