You may not consider yourself a drug dealer, but there are so many variables and circumstances that it could be a bit of a lottery.
First you haven’t drawn up any conditions upon the discovery of the cannabis.
Lets say you were caught out on a speeding offence and further inspection of your car revealed an amount of the drug.
If this was already in a state of current use then you would likely get a warning, possibly a summons, maybe a relatively small fine, but you would then be on record for that offence if it came to notice again.
If it was in packages of uniform amounts, or multiples of uniform amounts then someone is going to be very interested, the actual quantity is less important below say 8 or 9 ounces than the means of storage.
If you were searched as a result of an overall police investigation of another dealer then you could be in some bother.Your name may be dropped into the hat to try get someone a reduced prison sentence, and that person could say anything they wanted.
Police would look for other evidence of dealing, bank accounts, computors, maually held records, mobile phones and pagers, frequent changes of phones, cars and less easily accountable ways of cleaning up money such as betting slips, lottery tickets(you buy winning tickets at more than the value of the prize).
If you have any connections with known criminals, even low level ones this may prompt further suspicion, and in any case, the police will almost certainly be interested in where you obtained the drugs, using the threat of serious charges to counter the possibility on non-disclosure on your part.
Your advancing of money to buy drugs on behalf of another is certainly dealing, its just that in your case it is at a very low level, and it could be interpreted in all sorts of ways just to put pressure on you.
I’m afraid that you should be far more careful and less sympathetic, you should always look at the possible consequencies for yourself and balance those against the favours you are doing for others.
Think about what might happen if you have a simple fall out or differance of opinion with someone who owes you even a small amount of money, all kinds of crap could happen that you cannot predict.
In short, if you should look on this as something you do for yourself only, if someone else wants cannabis they should get it themselves, and if you want to roll a few friends a joint every now and then then fair enough, as long as the favour is returned, but be very careful if you do anything that could be construed as distribution, which even if it is not for profit can attract charges completely separate from those of drug dealing.